### 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
public void testUpdateTransferRightsSecondaryAuthHeaders() throws Exception {
        updateTransferRightsTester(true);
    }
    public void testUpdateThatChangesSettingsButNotHeaders() throws Exception {
        String transformId = "test_update_that_changes_settings";
        String destIndex = transformId + "-dest";
        
        createPivotReviewsTransform(transformId, destIndex, null, null, null);
        Request updateTransformRequest = createRequestWithAuth("POST", getTransformEndpoint() + transformId + "/_update", null);
        updateTransformRequest.setJsonEntity("""
            { "settings": { "max_page_search_size": 123 } }""");
        
        Map<String, Object> updatedConfig = entityAsMap(client().performRequest(updateTransformRequest));
        
        assertThat(updatedConfig.get("settings"), is(equalTo(Map.of("max_page_search_size", 123))));
    }
    private void updateTransferRightsTester(boolean useSecondaryAuthHeaders) throws Exception {
        String transformId = "transform1";
        
        
        
        String transformIdCloned = "transform2";
        String transformDest = transformId + "_idx";
        setupDataAccessRole(DATA_ACCESS_ROLE, REVIEWS_INDEX_NAME, transformDest);
        setupDataAccessRole(DATA_ACCESS_ROLE_2, REVIEWS_INDEX_NAME, transformDest);
        final Request createTransformRequest = useSecondaryAuthHeaders
            ? createRequestWithSecondaryAuth(
                "PUT",
                getTransformEndpoint() + transformId,
                BASIC_AUTH_VALUE_TRANSFORM_ADMIN_NO_DATA,