Bump actions/checkout from 3 to 4 (#998)

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

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Gregor Zeitlinger <[email protected]>

Author: dependabot[bot]

.github/workflows/github-pages.yaml

@@ -55,7 +55,7 @@ jobs:
       #- name: Install Dart Sass
       #  run: sudo snap install dart-sass
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           submodules: recursive
           fetch-depth: 0