test: Silence return_immediately flag Deprecation Warning (#1066)

Author: mukund-ananthu

pytest.ini

@@ -7,4 +7,6 @@ filterwarnings =
     # Remove once https://github.com/grpc/grpc/issues/35086 is fixed
     ignore:There is no current event loop:DeprecationWarning:grpc.aio._channel
     # Remove after support for Python 3.7 is dropped
-    ignore:After January 1, 2024, new releases of this library will drop support for Python 3.7:DeprecationWarning
+    ignore:After January 1, 2024, new releases of this library will drop support for Python 3.7:DeprecationWarning
+    # Remove warning once https://github.com/googleapis/python-pubsub/issues/1067 is fixed
+    ignore:The return_immediately flag is deprecated and should be set to False.:DeprecationWarning