Bump avsm/setup-ocaml from 2 to 3 (Deducteam#1125)

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

---
updated-dependencies:
- dependency-name: avsm/setup-ocaml
  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>

.github/workflows/main.yml

@@ -19,7 +19,7 @@ jobs:
           path: ~/.opam
           key: ${{ runner.os }}-ocaml-${{ matrix.ocaml-version }}
       - name: setting up opam ...
-        uses: avsm/setup-ocaml@v2
+        uses: avsm/setup-ocaml@v3
         with:
           ocaml-compiler: ${{ matrix.ocaml-version }}
       - name: installing dependencies ...