Fix flaky test with transactions (#7187)

* Fix flaky test with transactions

* Add CHANGELOG entry

* Fix the other transactions related tests that became flaky because now Parse Server tries to submit the transaction multilpe times in the case of TransientError

* Remove fit from tests

src/Adapters/Storage/Mongo/MongoStorageAdapter.js

@@ -1046,9 +1046,20 @@ export class MongoStorageAdapter implements StorageAdapter {
   }
 
   commitTransactionalSession(transactionalSection: any): Promise<void> {
-    return transactionalSection.commitTransaction().then(() => {
-      transactionalSection.endSession();
-    });
+    const commit = retries => {
+      return transactionalSection
+        .commitTransaction()
+        .catch(error => {
+          if (error && error.hasErrorLabel('TransientTransactionError') && retries > 0) {
+            return commit(retries - 1);
+          }
+          throw error;
+        })
+        .then(() => {
+          transactionalSection.endSession();
+        });
+    };
+    return commit(5);
   }
 
   abortTransactionalSession(transactionalSection: any): Promise<void> {