[github] Avoid deprecated parameter

```
:param login_or_token: string deprecated, use auth=github.Auth.Login(...) or auth=github.Auth.Token(...) instead
```

snapshot_manager/snapshot_manager/github_util.py

@@ -49,7 +49,8 @@ def __init__(self, config: config.Config, github_token: str = None, **kwargs):
         self.config = config
         if github_token is None:
             github_token = os.getenv(self.config.github_token_env)
-        self.github = github.Github(login_or_token=github_token)
+        auth = github.Auth.Token(github_token)
+        self.github = github.Github(auth=auth)
         self.gql = github_graphql.GithubGraphQL(token=github_token, raise_on_error=True)
         self.__label_cache = None
         self.__repo_cache = None