Fix macos CI

Author: xavierleroy

.github/workflows/build.yml

@@ -56,8 +56,7 @@ jobs:
           submodules: true
       - name: OS dependencies
         run: |
-          brew install coq ocaml
-          brew install --build-from-source menhir  # temporary workaround
+          brew install coq ocaml menhir
       - name: Configure
         run: tools/runner.sh configure
       - name: Build