fix(dev-infra): properly determine oauth scopes for git client token (#37462)

Resubmit of b2bd38699b since
85b6c94cc6 accidentally reverted
the fix due to rebasing most likely.

PR Close #37462

dev-infra/utils/git.ts

@@ -60,7 +60,7 @@ export class GitClient {
   /** The file path of project's root directory. */
   private _projectRoot = getRepoBaseDir();
   /** The OAuth scopes available for the provided Github token. */
-  private _oauthScopes = Promise.resolve<string[]>([]);
+  private _oauthScopes: Promise<string[]>|null = null;
   /** Regular expression that matches the provided Github token. */
   private _tokenRegex = new RegExp(this._githubToken, 'g');