[auth.py] Fix quoting of scopes

Scopes needs to be passed as a single CLI argument

Bug: b/351046856
Change-Id: I1c0e78b9bfa9997af3466f5b54ae27a535fa7488
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5689095
Commit-Queue: Yiwei Zhang <yiwzhang@google.com>
Reviewed-by: Yiwei Zhang <yiwzhang@google.com>
Auto-Submit: Allen Li <ayatane@chromium.org>

auth.py

@@ -49,7 +49,7 @@ class LoginRequiredError(Exception):
     """Interaction with the user is required to authenticate."""
     def __init__(self, scopes=OAUTH_SCOPE_EMAIL):
         msg = ('You are not logged in. Please login first by running:\n'
-               '  luci-auth login -scopes %s' % scopes)
+               '  luci-auth login -scopes "%s"' % scopes)
         super(LoginRequiredError, self).__init__(msg)