Fix: Datastore client: Mark test as flaky (GoogleCloudPlatform#8227)

Author: Mariatta

datastore/cloud-client/admin_test.py

@@ -42,6 +42,7 @@ def test_get_index(self):
     def test_list_index(self):
         assert admin.list_indexes(PROJECT)
 
+    @pytest.mark.flaky
     @backoff.on_exception(backoff.expo, (RetryError, TimeoutError), max_tries=3)
     def test_export_import_entities(self):
         response = admin.export_entities(PROJECT, "gs://" + BUCKET)