Bump redhat-plumbers-in-action/differential-shellcheck

Bumps [redhat-plumbers-in-action/differential-shellcheck](https://github.com/redhat-plumbers-in-action/differential-shellcheck) from 5.3.0 to 5.4.0.
- [Release notes](https://github.com/redhat-plumbers-in-action/differential-shellcheck/releases)
- [Changelog](https://github.com/redhat-plumbers-in-action/differential-shellcheck/blob/main/docs/CHANGELOG.md)
- [Commits](redhat-plumbers-in-action/differential-shellcheck@60c9f2b...cc6721c)

---
updated-dependencies:
- dependency-name: redhat-plumbers-in-action/differential-shellcheck
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/differential-shellcheck.yml

@@ -21,6 +21,6 @@ jobs:
           fetch-depth: 0
 
       - name: Differential ShellCheck
-        uses: redhat-plumbers-in-action/differential-shellcheck@60c9f2b924a9c5a2ddbb25e7b23e8e11b56faab9
+        uses: redhat-plumbers-in-action/differential-shellcheck@cc6721c45a8800cc666de45493545a07a638d121
         with:
           token: ${{ secrets.GITHUB_TOKEN }}