[CI] 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/ci.yml

@@ -41,7 +41,7 @@ jobs:
         - os: macOS-latest
           ghc: 'latest'
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - uses: haskell/actions/setup@v2.4.1
       id: setup-haskell-cabal
       with:
@@ -103,7 +103,7 @@ jobs:
   #  # See <https://github.com/vmactions/freebsd-vm#under-the-hood>
   #  runs-on: macos-latest
   #  steps:
-  #  - uses: actions/checkout@v3
+  #  - uses: actions/checkout@v4
   #  - name: Test
   #    id: build-freebsd
   #    uses: vmactions/freebsd-vm@v0.1.5