Fix warning about unfinished oauth tasks on shutdown (#141969)

* Don't wait for OAuth token task on shutdown

To reproduce the warning:
1. Start authentication with integration using OAuth (e.g. SmartThings)
2. When redirected to external login site, just close the page
3. Settings -> Restart Home Assistant

* Clarify comment

---------

Co-authored-by: Martin Hjelmare <marhje52@gmail.com>

homeassistant/components/cloud/account_link.py

@@ -127,7 +127,11 @@ class CloudOAuth2Implementation(config_entry_oauth2_flow.AbstractOAuth2Implement
                     flow_id=flow_id, user_input=tokens
                 )
 
-        self.hass.async_create_task(await_tokens())
+        # It's a background task because it should be cancelled on shutdown and there's nothing else
+        # we can do in such case. There's also no need to wait for this during setup.
+        self.hass.async_create_background_task(
+            await_tokens(), name="Awaiting OAuth tokens"
+        )
 
         return authorize_url