gitlab-runner: bump version to v16.8.1.
GitLab server was upgraded to 16.8, so also bump the gitlab-runner version.
Bug: T361165
How to register an account on GitLab. To prevent spam, new accounts are locked until approved by an admin or the approver bot. You can also file an unlock request to expedite access.
Support: mw:GitLab, how to host a project on GitLab, #wikimedia-gitlab on libera.chat, #GitLab on Phabricator.
GitLab server was upgraded to 16.8, so also bump the gitlab-runner version.
Bug: T361165