github: fix config mistake preventing repo lockdown commenting

github: fix config mistake preventing repo lockdown commenting

The previous commit updated the repo lockdown config to the new
format:

  commit 9b89cdb2a5064a87b8a7172fa1748d46aa37a9df
  Author: Alex Bennée <alex.bennee@linaro.org>
  Date:   Mon Oct 4 16:43:08 2021 +0100

    .github: move repo lockdown to the v2 configuration

Unfortunately the config key names used were wrong, resulting in
the repo lockdown throwing warnings:

  Unexpected input(s) 'pull-comment', 'lock-pull', 'close-pull',
  valid inputs are ['github-token', 'exclude-issue-created-before',
  'exclude-issue-labels', 'issue-labels', 'issue-comment',
  'skip-closed-issue-comment', 'close-issue', 'lock-issue',
  'issue-lock-reason', 'exclude-pr-created-before', 'exclude-pr-labels',
  'pr-labels', 'pr-comment', 'skip-closed-pr-comment', 'close-pr',
  'lock-pr', 'pr-lock-reason', 'process-only', 'log-output']

It still locked down the pull requests, due to its default config,
but didn't leave the friendly message explaining why.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>