[auth] Fix luci-auth reference in comment

Unfixed when we migrated Gerrit auth to git-credential-luci

Bug: b/342261857
Change-Id: I6660f03de830337b14b822a0245f6e0d18a58366
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6174308
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>
Commit-Queue: Allen Li <ayatane@chromium.org>

gerrit_util.py

@@ -876,8 +876,8 @@ class GitCredsAuthenticator(_Authenticator):
     def gerrit_account_exists(cls, host: str) -> bool:
         """Return True if the Gerrit account exists.
 
-        This checks the user currently logged in with luci-auth.
-        If the user is not logged in with luci-auth, returns False.
+        This checks the user currently logged in with git-credential-luci.
+        If the user is not logged in with git-credential-luci, returns False.
 
         This method caches positive results in the user's Git config.
         """