add matrix

Author: miorel

.github/workflows/run-tests.yml

@@ -5,8 +5,12 @@ on:
     types: [opened, synchronize]
 
 jobs:
-  lint:
-    runs-on: ubuntu-latest
+  run-tests:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
 
     steps:
       - name: Check out repository