ref(client): Fix mypy errors

GH-4601

Author: srothh

sentry_sdk/api.py

@@ -227,11 +227,11 @@ def flush(
 
 
 @clientmethod
-def flush_async(
+async def flush_async(
     timeout: Optional[float] = None,
     callback: Optional[Callable[[int, float], None]] = None,
 ) -> None:
-    return get_client().flush_async(timeout=timeout, callback=callback)
+    return await get_client().flush_async(timeout=timeout, callback=callback)
 
 
 def start_span(**kwargs: Any) -> Span:

sentry_sdk/client.py

@@ -982,7 +982,9 @@ async def close_async(
                 return
             await self.flush_async(timeout=timeout, callback=callback)
             self._close_components()
-            await self.transport.kill()
+            kill_task = self.transport.kill()  # type: ignore
+            if kill_task is not None:
+                await kill_task
             self.transport = None
 
     def flush(