Bump peaceiris/actions-gh-pages from 3 to 4

Bumps [peaceiris/actions-gh-pages](https://github.com/peaceiris/actions-gh-pages) from 3 to 4.
- [Release notes](https://github.com/peaceiris/actions-gh-pages/releases)
- [Changelog](https://github.com/peaceiris/actions-gh-pages/blob/main/CHANGELOG.md)
- [Commits](peaceiris/actions-gh-pages@v3...v4)

---
updated-dependencies:
- dependency-name: peaceiris/actions-gh-pages
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/docs.yml

@@ -62,7 +62,7 @@ jobs:
         name: bluesky_training-docs
         path: ${{ steps.deployment.outputs.artifact }}
 
-    - uses: peaceiris/actions-gh-pages@v3
+    - uses: peaceiris/actions-gh-pages@v4
       if: ${{ github.event.inputs.deploy }}
       with:
         github_token: ${{ secrets.GITHUB_TOKEN }}