build(deps): bump actions/checkout from 4 to 6 (#36)

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Author: dependabot[bot]

.github/workflows/ocaml.yml

@@ -14,7 +14,7 @@ jobs:
             with-doc: true
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: RedPRL/actions-ocaml@v2
         with:
           ocaml-compiler: ${{ matrix.ocaml-compiler }}