ci: Test on macos as well

Author: akirak

.github/workflows/ci.yml

@@ -9,7 +9,12 @@ on:
 
 jobs:
   check:
-    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        os:
+        - ubuntu-latest
+        - macos-latest
+    runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v4
     - uses: cachix/install-nix-action@v26