I think this test started failing when #96224 got merged?

**Build scan:**
https://gradle-enterprise.elastic.co/s/eocgfxmszp332/tests/:server:test/org.elasticsearch.search.internal.ShardSearchRequestTests/testForceSyntheticUnsupported

**Reproduction line:**
```
./gradlew ':server:test' --tests "org.elasticsearch.search.internal.ShardSearchRequestTests.testForceSyntheticUnsupported" -Dtests.seed=682CDD108409D789 -Dtests.locale=sv -Dtests.timezone=Asia/Ulan_Bator -Druntime.java=20
```

**Applicable branches:**
main

**Reproduces locally?:**
Yes

**Failure history:**
https://gradle-enterprise.elastic.co/scans/tests?tests.container=org.elasticsearch.search.internal.ShardSearchRequestTests&tests.test=testForceSyntheticUnsupported

**Failure excerpt:**
```
org.junit.ComparisonFailure: expected:<[cannot serialize [sub_searches] to version [8030099]]> but was:<[force_synthetic_source is not supported before 8.4.0]>

  at __randomizedtesting.SeedInfo.seed([682CDD108409D789:84F9A71AB60DC34F]:0)
  at org.junit.Assert.assertEquals(Assert.java:115)
  at org.junit.Assert.assertEquals(Assert.java:144)
  at org.elasticsearch.search.internal.ShardSearchRequestTests.testForceSyntheticUnsupported(ShardSearchRequestTests.java:270)
  at jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
  at java.lang.reflect.Method.invoke(Method.java:578)
  at com.carrotsearch.randomizedtesting.RandomizedRunner.invoke(RandomizedRunner.java:1758)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$8.evaluate(RandomizedRunner.java:946)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$9.evaluate(RandomizedRunner.java:982)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$10.evaluate(RandomizedRunner.java:996)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.tests.util.TestRuleSetupTeardownChained$1.evaluate(TestRuleSetupTeardownChained.java:48)
  at org.apache.lucene.tests.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:43)
  at org.apache.lucene.tests.util.TestRuleThreadAndTestName$1.evaluate(TestRuleThreadAndTestName.java:45)
  at org.apache.lucene.tests.util.TestRuleIgnoreAfterMaxFailures$1.evaluate(TestRuleIgnoreAfterMaxFailures.java:60)
  at org.apache.lucene.tests.util.TestRuleMarkFailure$1.evaluate(TestRuleMarkFailure.java:44)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$StatementRunner.run(ThreadLeakControl.java:390)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl.forkTimeoutingTask(ThreadLeakControl.java:843)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$3.evaluate(ThreadLeakControl.java:490)
  at com.carrotsearch.randomizedtesting.RandomizedRunner.runSingleTest(RandomizedRunner.java:955)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$5.evaluate(RandomizedRunner.java:840)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$6.evaluate(RandomizedRunner.java:891)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$7.evaluate(RandomizedRunner.java:902)
  at org.apache.lucene.tests.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:43)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.tests.util.TestRuleStoreClassName$1.evaluate(TestRuleStoreClassName.java:38)
  at com.carrotsearch.randomizedtesting.rules.NoShadowingOrOverridesOnMethodsRule$1.evaluate(NoShadowingOrOverridesOnMethodsRule.java:40)
  at com.carrotsearch.randomizedtesting.rules.NoShadowingOrOverridesOnMethodsRule$1.evaluate(NoShadowingOrOverridesOnMethodsRule.java:40)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.tests.util.TestRuleAssertionsRequired$1.evaluate(TestRuleAssertionsRequired.java:53)
  at org.apache.lucene.tests.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:43)
  at org.apache.lucene.tests.util.TestRuleMarkFailure$1.evaluate(TestRuleMarkFailure.java:44)
  at org.apache.lucene.tests.util.TestRuleIgnoreAfterMaxFailures$1.evaluate(TestRuleIgnoreAfterMaxFailures.java:60)
  at org.apache.lucene.tests.util.TestRuleIgnoreTestSuites$1.evaluate(TestRuleIgnoreTestSuites.java:47)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$StatementRunner.run(ThreadLeakControl.java:390)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl.lambda$forkTimeoutingTask$0(ThreadLeakControl.java:850)
  at java.lang.Thread.run(Thread.java:1623)

```
server/src/main/java/org/elasticsearch/search/builder/SearchSourceBuilder.java
public static final ParseField _SOURCE_FIELD = new ParseField("_source");
    public static final ParseField STORED_FIELDS_FIELD = new ParseField("stored_fields");
    public static final ParseField DOCVALUE_FIELDS_FIELD = new ParseField("docvalue_fields");
    public static final ParseField FETCH_FIELDS_FIELD = new ParseField("fields");
    public static final ParseField SCRIPT_FIELDS_FIELD = new ParseField("script_fields");
    public static final ParseField SCRIPT_FIELD = new ParseField("script");
    public static final ParseField IGNORE_FAILURE_FIELD = new ParseField("ignore_failure");
    public static final ParseField SORT_FIELD = new ParseField("sort");
    public static final ParseField TRACK_SCORES_FIELD = new ParseField("track_scores");
    public static final ParseField TRACK_TOTAL_HITS_FIELD = new ParseField("track_total_hits");
    public static final ParseField INDICES_BOOST_FIELD = new ParseField("indices_boost");
    public static final ParseField AGGREGATIONS_FIELD = new ParseField("aggregations");
    public static final ParseField AGGS_FIELD = new ParseField("aggs");
    public static final ParseField HIGHLIGHT_FIELD = new ParseField("highlight");
    public static final ParseField SUGGEST_FIELD = new ParseField("suggest");
    public static final ParseField RESCORE_FIELD = new ParseField("rescore");
    public static final ParseField STATS_FIELD = new ParseField("stats");
    public static final ParseField EXT_FIELD = new ParseField("ext");
    public static final ParseField PROFILE_FIELD = new ParseField("profile");
    public static final ParseField SEARCH_AFTER = new ParseField("search_after");
    public static final ParseField COLLAPSE = new ParseField("collapse");
    public static final ParseField SLICE = new ParseField("slice");
    public static final ParseField POINT_IN_TIME = new ParseField("pit");
    public static final ParseField RUNTIME_MAPPINGS_FIELD = new ParseField("runtime_mappings");
    /**
     * A static factory method to construct a new search source.
     */
    public static SearchSourceBuilder searchSource() {
        return new SearchSourceBuilder();
    }