python: address telemetry review nits

- Use asyncio.create_task instead of the legacy asyncio.ensure_future when
  scheduling awaitable notification handlers on the event loop thread.
- Drop the redundant local `import asyncio` in the telemetry transport test
  (asyncio is already imported at module scope), clearing CodeQL
  py/repeated-import.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: MackinnonBuck

python/copilot/_jsonrpc.py

@@ -463,7 +463,7 @@ async def _await_outcome():
                 except Exception:  # pylint: disable=broad-except
                     logger.warning("Notification handler raised", exc_info=True)
 
-            asyncio.ensure_future(_await_outcome())
+            asyncio.create_task(_await_outcome())
 
     async def _dispatch_request(self, message: dict, handler: RequestHandler):
         try:

python/test_client.py

@@ -2342,8 +2342,6 @@ async def mock_request(method, params, **kwargs):
 
     @pytest.mark.asyncio
     async def test_event_routes_to_handler_via_notification_transport(self):
-        import asyncio
-
         from copilot.generated.rpc import GitHubTelemetryNotification
 
         received: list = []