stop and join watchdog observer (#11706)

This is in accordance with the example.  For inotify at least the `.stop()`
call ends up calling the removed unschedule call anyways.

72f2eb7203 (example-api-usage)

chia/util/file_keyring.py

@@ -174,7 +174,8 @@ class FileKeyring(FileSystemEventHandler):
 
     def cleanup_keyring_file_watcher(self):
         if getattr(self, "keyring_observer"):
-            self.keyring_observer.unschedule_all()
+            self.keyring_observer.stop()
+            self.keyring_observer.join()
 
     def on_modified(self, event):
         self.check_if_keyring_file_modified()