Add custom exception for bad GitHub access tokens

Author: penyuan

oshminer/errors/exceptions.py

@@ -3,6 +3,9 @@
 # SPDX-FileCopyrightText: 2022 Pen-Yuan Hsing
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
+class BadGitHubTokenError(Exception): 
+    pass
+
 class BadRepoError(Exception): 
     pass