### Elasticsearch Version

main

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

MacOS

### Problem Description

When there are 2 or more concurrent `_update` requests issued, one of them may fail with `ResourceAlreadyExistsException` exception which is misleading.


### Steps to Reproduce

1. Spawn a number of `_update` requests at the same time
2. Look at the results of these requests
3. Observe `ResourceAlreadyExistsException` being thrown in the case of conflict

### Logs (if relevant)

_No response_
x-pack/plugin/transform/qa/single-node-tests/src/javaRestTest/java/org/elasticsearch/xpack/transform/integration/TransformUpdateIT.java
BASIC_AUTH_VALUE_TRANSFORM_ADMIN_2
            )
            : createRequestWithAuth("PUT", getTransformEndpoint() + transformId, BASIC_AUTH_VALUE_TRANSFORM_ADMIN_2);
        final Request createTransformRequest_2 = useSecondaryAuthHeaders
            ? createRequestWithSecondaryAuth(
                "PUT",
                getTransformEndpoint() + transformIdCloned,
                BASIC_AUTH_VALUE_TRANSFORM_ADMIN_NO_DATA,
                BASIC_AUTH_VALUE_TRANSFORM_ADMIN_2
            )
            : createRequestWithAuth("PUT", getTransformEndpoint() + transformIdCloned, BASIC_AUTH_VALUE_TRANSFORM_ADMIN_2);
        String config = Strings.format("""
            {
              "dest": {
                "index": "%s"
              },
              "source": {
                "index": "%s"
              },
              "pivot": {
                "group_by": {
                  "reviewer": {
                    "terms": {
                      "field": "user_id"
                    }
                  }
                },
                "aggregations": {
                  "avg_rating": {
                    "avg": {