Fix

- TypeError: 'ABCMeta' object is not subscriptable
- AttributeError: partially initialized module 'firebase_admin._user_mgt' has no attribute 'UserMetadata' (most likely due to a circular import)
- db.Reference signature

Author: ViktorSky

firebase_admin/credentials.py

@@ -32,7 +32,7 @@
 else:
     import os
 
-    StrPath = typing.Union[str, os.PathLike[str]]
+    StrPath = typing.Union[str, 'os.PathLike[str]']
 
 
 _request = requests.Request()