chore(deps): update reviewdog/action-shellcheck action to v1.21

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
reviewdog/action-shellcheck	action	minor	v1.20 -> v1.21

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Release Notes

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

### [`v1.21`](https://togithub.com/reviewdog/action-shellcheck/compare/v1.20...v1.21) [Compare Source](https://togithub.com/reviewdog/action-shellcheck/compare/v1.20...v1.21)

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Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 Automerge: Enabled.

♻ Rebasing: Whenever PR is behind base branch, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about this update again.

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

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