CI: use recent ocaml action

Author: c-cube

.github/workflows/build.yml

@@ -39,7 +39,7 @@ jobs:
       - uses: actions/checkout@v3
 
       - name: Use OCaml ${{ matrix.ocaml-compiler }}
-        uses: ocaml/setup-ocaml@v2
+        uses: ocaml/setup-ocaml@v3
         with:
           ocaml-compiler: ${{ matrix.ocaml-compiler }}
           opam-depext-flags: --with-test