[container-registry] fix: mark a flaky test [(#3765)](#3765)

fixes #2894

Author: Takashi Matsuo

container_registry/container_analysis/snippets/samples_test.py

@@ -29,6 +29,7 @@
 from grafeas.grafeas_v1.gapic.enums import NoteKind
 from grafeas.grafeas_v1.gapic.enums import Severity
 from grafeas.grafeas_v1.gapic.enums import Version
+import pytest
 
 import samples
 
@@ -145,6 +146,7 @@ def test_occurrences_for_note(self):
         # clean up
         samples.delete_occurrence(basename(occ.name), PROJECT_ID)
 
+    @pytest.mark.flaky(max_runs=3, min_passes=1)
     def test_pubsub(self):
         # create topic if needed
         client = SubscriberClient()