fix: address backwards compatibility warnings failing presubmits

Author: vchudnov-g

google/api_core/retry/retry_streaming_async.py

@@ -160,9 +160,14 @@ async def retry_target_stream(
                     # bare except catches any exception passed to `athrow`
                     if target_is_generator:
                         # delegate error handling to target_iterator
-                        await cast(AsyncGenerator["_Y", None], target_iterator).athrow(
-                            *sys.exc_info()
-                        )
+
+                        # TODO: Remove this conditional once the minimum supported Python version is 3.11
+                        if sys.version_info[:3] >= (3, 11, 0):
+                            await cast(AsyncGenerator["_Y", None], target_iterator).athrow(
+                                sys.exception())
+                        else:
+                            await cast(AsyncGenerator["_Y", None], target_iterator).athrow(
+                                *sys.exc_info())
                     else:
                         raise
             return

tests/asyncio/retry/test_retry_streaming_async.py

@@ -201,7 +201,7 @@ async def test___call___generator_cancellations(self):
         """
         # test without cancel as retryable
         retry_ = retry_streaming_async.AsyncStreamingRetry()
-        utcnow = datetime.datetime.utcnow()
+        utcnow = datetime.datetime.now(datetime.timezone.utc)
         mock.patch("google.api_core.datetime_helpers.utcnow", return_value=utcnow)
         generator = await retry_(self._generator_mock)(sleep_time=0.2)
         assert await generator.__anext__() == 0