Revert "Fix macos CI"

The Homebrew precompiled binaries for Menhirlib are outdated, let's try building from source again.

This reverts commit 25b9fc8.

Author: xavierleroy

.github/workflows/build.yml

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