intermittent fix (hapifhir#6751)

Author: TipzCM

hapi-fhir-jpaserver-test-r4/src/test/java/ca/uhn/fhir/jpa/bulk/BulkDataExportTest.java

@@ -454,7 +454,7 @@ public void testBulkExportParametersPersistExtraData() {
 		String value = "value_";
 		options.setUserData(key, value);
 
-		List<String> valueSet = new ArrayList<>();
+		List<String> valueSet = Collections.synchronizedList(new ArrayList<>());
 		Object interceptor = new Object() {
 			@Hook(Pointcut.STORAGE_BULK_EXPORT_RESOURCE_INCLUSION)
 			public void onExpandResources(IBaseResource theBaseResource, BulkExportJobParameters theParams) {