ci: run the test suite on ubuntu, macOS and Windows

Author: dannywillems

.github/workflows/ci.yml

@@ -59,11 +59,13 @@ jobs:
         run: make typecheck
 
   test:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
     needs: [lint, typecheck]
     strategy:
+      fail-fast: false
       matrix:
         python-version: ["3.11", "3.12", "3.13", "3.14"]
+        os: [ubuntu-latest, macos-latest, windows-latest]
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
@@ -77,6 +79,10 @@ jobs:
         with:
           python-version: ${{ matrix.python-version }}
 
+      - name: Install GNU sed on macOS
+        if: runner.os == 'macOS'
+        run: brew install gnu-sed
+
       - name: Install dependencies
         run: make setup