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] <[email protected]>

.github/workflows/main.yml

@@ -31,7 +31,7 @@ jobs:
         run: mvn clean verify
       - name: Publish Nightly Update Site
         if: github.event_name != 'release' && github.ref == 'refs/heads/main' && github.repository_owner == 'DataFlowAnalysis'
-        uses: peaceiris/actions-gh-pages@v3
+        uses: peaceiris/actions-gh-pages@v4
         with:
           deploy_key: ${{ secrets.UPDATE_SITE_DEPLOY_KEY }}
           external_repository: DataFlowAnalysis/updatesite
@@ -40,7 +40,7 @@ jobs:
           publish_branch: main
       - name: Publish Release Update Site
         if: github.event_name == 'release' && github.repository_owner == 'DataFlowAnalysis'
-        uses: peaceiris/actions-gh-pages@v3
+        uses: peaceiris/actions-gh-pages@v4
         with:
           deploy_key: ${{ secrets.UPDATE_SITE_DEPLOY_KEY }}
           external_repository: DataFlowAnalysis/updatesite