CI: Add z3 package to macOS as a test dependency of c2rust-refactor

Author: ahomescu

.github/workflows/ci.yml

@@ -92,7 +92,7 @@ jobs:
         run: |
           # `cmake` needed, but should be already installed.
           # `bash` needed b/c macOS ships with bash 3, which doesn't support arrays properly.
-          brew install -q ninja gpg llvm@${{ matrix.clang-version }} bash
+          brew install -q ninja gpg llvm@${{ matrix.clang-version }} bash z3
 
       - name: cargo build --release
         run: |