Bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/js_of_ocaml.yml

@@ -103,7 +103,7 @@ jobs:
         run: sudo apt-get update
 
       - name: Checkout tree
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
         # EJGA: Note that I tried to fix this upstream as depext is
         # getting much better, but no luck yet, c.f:

.github/workflows/lint.yml

@@ -16,7 +16,7 @@ jobs:
       - name: Update apt cache
         run: sudo apt-get update
       - name: Checkout tree
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Set-up OCaml
         uses: ocaml/setup-ocaml@v3
         with:
@@ -34,7 +34,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout tree
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Set-up OCaml
         uses: ocaml/setup-ocaml@v3
         with:
@@ -45,7 +45,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout tree
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Set-up Biome
         uses: biomejs/setup-biome@v2
         with:

.github/workflows/wasm_of_ocaml.yml

@@ -71,13 +71,13 @@ jobs:
         run: sudo apt-get update
 
       - name: Checkout tree
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           path: wasm_of_ocaml
 
       - name: Checkout Jane Street opam repository
         if: matrix.jane_street_tests
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           repository: janestreet/opam-repository
           ref: 2819773f29b6f6c14b918eae3cb40c8ff6b22d0e