[gerrit_util] Fix typo

Bug: b/351039944
Change-Id: If906ddfdae10b6ba9051eced2b1e7a2c24d54aad
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5677486
Reviewed-by: Yiwei Zhang <yiwzhang@google.com>
Auto-Submit: Allen Li <ayatane@chromium.org>
Commit-Queue: Yiwei Zhang <yiwzhang@google.com>

gerrit_util.py

@@ -275,7 +275,7 @@ class Authenticator(object):
                     if skip_sso:
                         LOGGER.debug(
                             'Authenticator.get: skipping SSOAuthenticator.')
-                        authenticators = authenticators[1:]
+                        a = a[1:]
                     ret = ChainedAuthenticator(a)
                 cls._resolved = ret
                 return ret