ci: add cross-platform testing in GitHub Actions workflow

Author: bartventer

.github/workflows/default.yml

@@ -11,7 +11,10 @@ defaults:
 jobs:
   test:
     name: Test
-    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
     env:
       OUTPUTDIR: coverage
       COVERPROFILE: coverage.out
@@ -35,4 +38,4 @@ jobs:
           files: ${{ env.OUTPUTDIR }}/${{ env.COVERPROFILE }}
           flags: unittests
           disable_search: true
-          verbose: true
+          verbose: true