chore(deps): update reviewdog/action-shellcheck action to v1.21.0

[stackable-bot]

This PR contains the following updates:

Package	Type	Update	Change
reviewdog/action-shellcheck	action	minor	v1.20.0 -> v1.21.0

---

Release Notes

reviewdog/action-shellcheck (reviewdog/action-shellcheck)

### [`v1.21.0`](https://togithub.com/reviewdog/action-shellcheck/releases/tag/v1.21.0) [Compare Source](https://togithub.com/reviewdog/action-shellcheck/compare/v1.20.0...v1.21.0) #### What's Changed - chore(deps): update reviewdog/reviewdog to 0.17.5 by [@​github-actions](https://togithub.com/github-actions) in [https://github.com/reviewdog/action-shellcheck/pull/59](https://togithub.com/reviewdog/action-shellcheck/pull/59) **Full Changelog**: https://github.com/reviewdog/action-shellcheck/compare/v1.20.0...v1.21.0

---

Configuration

📅 Schedule: Branch creation - "" in timezone Europe/Berlin, Automerge - At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

👻 Immortal: This PR will be recreated if closed unmerged. Get config help if that's undesired.

---

• [ ] If you want to rebase/retry this PR, check this box

---

This PR has been generated by Renovate Bot.