Bump actions/checkout from 3 to 4

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] <support@github.com>

.github/workflows/gh-pages.yml

@@ -25,7 +25,7 @@ jobs:
     name: Generate documentation
     runs-on: ubuntu-20.04
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           fetch-depth: 0
 
@@ -86,7 +86,7 @@ jobs:
             gh release edit -n "$DESC"
           fi
 
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         if: github.event_name == 'release' || github.event_name == 'push' || github.event_name == 'workflow_dispatch'
         with:
           ref: gh-pages