Bump peaceiris/actions-gh-pages from v3 to v3.8.0

Bumps [peaceiris/actions-gh-pages](https://github.com/peaceiris/actions-gh-pages) from v3 to v3.8.0.
- [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...068dc23)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Diff for: .github/workflows/generate_javadoc.yml

@@ -21,7 +21,7 @@ jobs:
     - name: Generate Javadoc
       run: ./gradlew javadoc
     - name: Push changes
-      uses: peaceiris/actions-gh-pages@v3
+      uses: peaceiris/actions-gh-pages@v3.8.0
       with: 
         github_token: ${{ secrets.GITHUB_TOKEN }}
         publish_dir: ./docs