Revert "[Python Aio] Replace get_event_loop() with new_event_loop() (#35493)"

This reverts commit d6579e32a0.

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

@@ -181,7 +181,7 @@ if PY_MAJOR_VERSION >= 3 and PY_MINOR_VERSION >= 7:
         try:
             return asyncio.get_running_loop()
         except RuntimeError:
-            return asyncio.get_event_loop_policy().new_event_loop()
+            return asyncio.get_event_loop_policy().get_event_loop()
 else:
     def get_working_loop():
         """Returns a running event loop."""