Add macOS ci

Author: pavelzw

.github/workflows/ci-copier.yml

@@ -7,10 +7,14 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
-  linux-unittests:
+  unittests:
     name: Check project generation
     timeout-minutes: 30
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        # ensure that `sed` behaves well on both Linux and macOS
+        os: [ubuntu-latest, macos-latest]
     steps:
       - name: Checkout
         uses: actions/checkout@v4