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] <[email protected]>

.github/workflows/ci.yml

@@ -66,7 +66,7 @@ jobs:
           echo "OPAM_FLAGS=$with_doc $with_test" >> "$GITHUB_ENV"
 
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Use OCaml ${{ matrix.ocaml }}
         if: matrix.bytecode != 'bytecode'
@@ -179,7 +179,7 @@ jobs:
               libyojson-ocaml-dev
 
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Try building
         run: make
@@ -238,7 +238,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Build Docker image
         run: |
@@ -296,7 +296,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Setup Nix
         uses: ./.github/composites/setup-nix
@@ -329,7 +329,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Setup Nix
         uses: ./.github/composites/setup-nix