ci: fix commit SHA for stefanbuck/github-issue-parser

ci: fix commit SHA for stefanbuck/github-issue-parser

The SHA for this action was updated by Dependabot in #25900 to a commit
which later disappeared from the repo. Since then Dependabot kept
(silently) failing to bump the SHA further:

updater | 2024/03/31 21:22:13 ERROR <job_807574419> Error processing stefanbuck/github-issue-parser (Dependabot::SharedHelpers::HelperSubprocessFailed)
updater | 2024/03/31 21:22:13 ERROR <job_807574419> error: no such commit c1a559d78bfb8dd05216dab9ffd2b91082ff5324

See: https://github.com/systemd/systemd/pull/25900#issuecomment-2028912672

Let's bump the SHA manually to v3.1.0 to get Dependabot back on the track.

Co-authored-by: Evgeny Vereshchagin <evvers@ya.ru>