GA(deps): Bump ocaml/setup-ocaml from 2 to 3

Bumps [ocaml/setup-ocaml](https://github.com/ocaml/setup-ocaml) from 2 to 3.
- [Release notes](https://github.com/ocaml/setup-ocaml/releases)
- [Changelog](https://github.com/ocaml/setup-ocaml/blob/master/CHANGELOG.md)
- [Commits](ocaml/setup-ocaml@v2...v3)

---
updated-dependencies:
- dependency-name: ocaml/setup-ocaml
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/ci.yaml

@@ -10,7 +10,7 @@ jobs:
         ocaml-version: [ '4.08.1', '4.09.1', '4.10.1', '4.11.2', '4.12.0']
     steps:
     - uses: actions/checkout@master
-    - uses: ocaml/setup-ocaml@v2
+    - uses: ocaml/setup-ocaml@v3
       with:
         ocaml-version: ${{ matrix.ocaml-version }}
     - run: |