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/hugo.yaml

@@ -19,7 +19,7 @@ jobs:
           hugo: 'true'
       - run: make web_zip
 
-      - uses: peaceiris/actions-gh-pages@v3
+      - uses: peaceiris/actions-gh-pages@v4
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_branch: _hugo

.github/workflows/slides.yaml

@@ -19,7 +19,7 @@ jobs:
           texlive: 'true'
       - run: make slides
 
-      - uses: peaceiris/actions-gh-pages@v3
+      - uses: peaceiris/actions-gh-pages@v4
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_branch: _slides