Executor/MaRS: The runner never gets re-registered if it got removed from the gitlab side

Because MaRS is being overly-cautious and never removes a token it cannot delete, MaRS fails to re-register a runner when the token was already invalidated.

Since we now have the runner ID stored, we should use it to check if the runner still exists and re-register the runner if this was not the case.

Sample logs:

Jun 10 09:06:28 mupuf-gateway executor[841]: 2023-06-10 09:06:28,044 [MarsClient] [WARNING] verify_or_renew_token: mupuf-gfx10-vangogh-5's freedesktop runner: The token 4frykQjURLRfL-pBy7hk is invalid. Starting the renewal process...
Jun 10 09:06:28 mupuf-gateway executor[841]: 2023-06-10 09:06:28,446 [MarsClient] [ERROR] remove_and_register: mupuf-gfx10-vangogh-5's freedesktop runner: Could not unregister the runner on freedesktop