build(deps): Bump specdown/setup-specdown-action from 0.2.20 to 0.2.21

Bumps [specdown/setup-specdown-action](https://github.com/specdown/setup-specdown-action) from 0.2.20 to 0.2.21.
- [Release notes](https://github.com/specdown/setup-specdown-action/releases)
- [Changelog](https://github.com/specdown/setup-specdown-action/blob/main/CHANGELOG.md)
- [Commits](specdown/setup-specdown-action@v0.2.20...v0.2.21)

---
updated-dependencies:
- dependency-name: specdown/setup-specdown-action
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

.github/workflows/ci.yaml

@@ -27,7 +27,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v4
-    - uses: specdown/setup-specdown-action@v0.2.20
+    - uses: specdown/setup-specdown-action@v0.2.21
     - name: Set up python ${{ env.PYTHON_VERSION }}
       id: setup-python
       uses: actions/setup-python@v4