Bump frenck/action-addon-linter from 2.18 to 2.21

Bumps [frenck/action-addon-linter](https://github.com/frenck/action-addon-linter) from 2.18 to 2.21.
- [Release notes](https://github.com/frenck/action-addon-linter/releases)
- [Commits](https://github.com/frenck/action-addon-linter/compare/v2.18...v2.21)

---
updated-dependencies:
- dependency-name: frenck/action-addon-linter
  dependency-version: '2.21'
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

.github/workflows/lint.yaml

@@ -36,6 +36,6 @@ jobs:
         uses: actions/checkout@v5
 
       - name: 🚀 Run Home Assistant Add-on Lint
-        uses: frenck/action-addon-linter@v2.18
+        uses: frenck/action-addon-linter@v2.21
         with:
           path: "./${{ matrix.path }}"