🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

google/cloud/errorreporting_v1beta1/services/error_group_service/async_client.py

@@ -427,7 +427,7 @@ async def sample_update_group():
         # Done; return the response.
         return response
 
-    async def __aenter__(self):
+    async def __aenter__(self) -> "ErrorGroupServiceAsyncClient":
         return self
 
     async def __aexit__(self, exc_type, exc, tb):

google/cloud/errorreporting_v1beta1/services/error_stats_service/async_client.py

@@ -597,7 +597,7 @@ async def sample_delete_events():
         # Done; return the response.
         return response
 
-    async def __aenter__(self):
+    async def __aenter__(self) -> "ErrorStatsServiceAsyncClient":
         return self
 
     async def __aexit__(self, exc_type, exc, tb):

google/cloud/errorreporting_v1beta1/services/report_errors_service/async_client.py

@@ -348,7 +348,7 @@ async def sample_report_error_event():
         # Done; return the response.
         return response
 
-    async def __aenter__(self):
+    async def __aenter__(self) -> "ReportErrorsServiceAsyncClient":
         return self
 
     async def __aexit__(self, exc_type, exc, tb):