Bump actions/checkout from 3 to 4 (#769)

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

.github/workflows/docs.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - uses: purcell/setup-emacs@master
         with:

.github/workflows/test.yml

@@ -62,7 +62,7 @@ jobs:
           wget https://github.com/rust-analyzer/rust-analyzer/releases/download/$RUST_ANALYZER_VERSION/rust-analyzer-linux -O $HOME/bin/rust-analyzer
           chmod +x $HOME/bin/rust-analyzer
 
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Run tests
         run: 'make ci'