ref(worker): Readd coroutine check for worker callbacks

The flush method in the transport enqueues a sync callback for the worker, therefore the check needs to be here after all.

GH-4581

Author: srothh

sentry_sdk/worker.py

@@ -3,6 +3,7 @@
 import os
 import threading
 import asyncio
+import inspect
 
 from time import sleep, time
 from sentry_sdk._queue import Queue, FullError
@@ -305,7 +306,11 @@ async def _target(self) -> None:
 
     async def _process_callback(self, callback: Callable[[], Any]) -> None:
         # Callback is an async coroutine, need to await it
-        await callback()
+        if inspect.iscoroutinefunction(callback):
+            await callback()
+        else:
+            # Callback is a sync function, such as _flush_client_reports()
+            callback()
 
     def _on_task_complete(self, task: asyncio.Task[None]) -> None:
         try: