run github action maven.yml also for macos

Windows is not included due to disk full on runs
diff --git a/.github/workflows/maven.yml b/.github/workflows/maven.yml
index 0d16a49..ff0e2e4 100644
--- a/.github/workflows/maven.yml
+++ b/.github/workflows/maven.yml
@@ -11,7 +11,12 @@
 jobs:
   build:
 
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest]
 
     steps:
     - uses: actions/checkout@v2