Bump actions/checkout from 3 to 4 (#1452)

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](https://github.com/actions/checkout/compare/v3...v4)

---
updated-dependencies:
- dependency-name: actions/checkout
  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>

.github/workflows/docs.yml

@@ -28,7 +28,7 @@ jobs:
       - name: Setup mdBook
         run: |
           cargo install mdbook --git https://github.com/Demonthos/mdBook.git --branch master
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Build
         run: cd docs &&