CI: move to setup-ocaml@v3 to work around problem on ubuntu 24.04

v2 tries to install darcs, which is not available on the ubuntu 24.04
runners.

Changes are from #2153, which failed mysteriously when it was filed
but might work better now.

Author: sauclovian-g

.github/workflows/ci.yml

@@ -489,9 +489,9 @@ jobs:
           chmod +x dist/bin/*
           echo $GITHUB_WORKSPACE/dist/bin >> $GITHUB_PATH
 
-      - uses: ocaml/setup-ocaml@v2
+      - uses: ocaml/setup-ocaml@v3
         with:
-          ocaml-compiler: 4.14.x
+          ocaml-compiler: "4.14"
 
       - run: opam repo add coq-released https://coq.inria.fr/opam/released