Bump peaceiris/actions-gh-pages from 3.9.3 to 4.0.0 (#1784)

Bumps [peaceiris/actions-gh-pages](https://github.com/peaceiris/actions-gh-pages) from 3.9.3 to 4.0.0.
- [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@373f7f2...4f9cc66)

---
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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/build-sphinx.yml

@@ -146,7 +146,7 @@ jobs:
       # The step is only used to build docs while pushing a PR to "master"
       - name: Deploy docs
         if: env.GH_EVENT_PUSH_UPSTREAM
-        uses: peaceiris/actions-gh-pages@373f7f263a76c20808c831209c920827a82a2847 # v3.9.3
+        uses: peaceiris/actions-gh-pages@4f9cc6602d3f66b9c108549d475ec49e8ef4d45e # v4.0.0
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ${{ env.PUBLISH_DIR }}
@@ -159,7 +159,7 @@ jobs:
       # The step is only used to build docs while pushing to PR branch
       - name: Publish pull-request docs
         if: env.GH_EVENT_OPEN_PR_UPSTREAM
-        uses: peaceiris/actions-gh-pages@373f7f263a76c20808c831209c920827a82a2847 # v3.9.3
+        uses: peaceiris/actions-gh-pages@4f9cc6602d3f66b9c108549d475ec49e8ef4d45e # v4.0.0
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ${{ env.PUBLISH_DIR }}