WIP: fix CI failure

Author: aykevl

.github/workflows/test.yml

@@ -18,6 +18,10 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v2
+      - name: install Clang
+        # Note: picking LLVM 15 because that's the one currently included in
+        # macos-latest. This probably needs an update in the future.
+        run: brew install llvm
       - name: Run tests
         run: make test CLANG=$(brew --prefix llvm)/bin/clang
   Test-Windows: