ref(worker): Remove loop upon killing worker

GH-4581

Author: srothh

sentry_sdk/worker.py

@@ -195,6 +195,7 @@ def kill(self) -> None:
             self._task.cancel()
             self._task = None
             self._task_for_pid = None
+            self._loop = None
 
     def start(self) -> None:
         if not self.is_alive: