Bump actions/checkout from 4 to 5 (#36)

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 5.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...v5)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '5'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/doc.yml

@@ -28,7 +28,7 @@ jobs:
 
     steps:
       - name: Checkout tree
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
 
       - name: Set-up OCaml
         uses: ocaml/setup-ocaml@v3

.github/workflows/workflow.yml

@@ -27,7 +27,7 @@ jobs:
 
     steps:
       - name: Checkout tree
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
 
       - name: Set-up OCaml
         uses: ocaml/setup-ocaml@v3
@@ -44,7 +44,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout tree
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
       - name: Set-up OCaml
         uses: ocaml/setup-ocaml@v3
         with:
@@ -55,7 +55,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout tree
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
       - name: Set-up OCaml
         uses: ocaml/setup-ocaml@v3
         with:
@@ -66,7 +66,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout tree
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
       - name: Set-up OCaml
         uses: ocaml/setup-ocaml@v3
         with: