Use context manager

src/python/grpcio/grpc/_cython/_cygrpc/aio/common.pyx.pxi

@@ -183,14 +183,15 @@ if PY_MAJOR_VERSION >= 3 and PY_MINOR_VERSION >= 7:
         try:
             return asyncio.get_running_loop()
         except RuntimeError:
-            # Convert warnings to errors so we can capture them with except
-            warnings.filterwarnings("error", category=DeprecationWarning, module=__name__)
-            try:
-                return asyncio.get_event_loop_policy().get_event_loop()
-            # Since version 3.12, DeprecationWarning is emitted if there is no
-            # current event loop.
-            except DeprecationWarning:
-                return asyncio.get_event_loop_policy().new_event_loop()
+            with warnings.catch_warnings():
+                # Convert DeprecationWarning to errors so we can capture them with except
+                warnings.simplefilter("error", DeprecationWarning)
+                try:
+                    return asyncio.get_event_loop_policy().get_event_loop()
+                # Since version 3.12, DeprecationWarning is emitted if there is no
+                # current event loop.
+                except DeprecationWarning:
+                    return asyncio.get_event_loop_policy().new_event_loop()
 else:
     def get_working_loop():
         """Returns a running event loop."""