Update unittests-mpich.yml

Author: jan-janssen

.github/workflows/unittests-mpich.yml

@@ -10,11 +10,21 @@ on:
 
 jobs:
   build:
-
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.operating-system }}
     strategy:
       matrix:
-        python-version: ['3.10', '3.11', '3.12']
+        include:
+        - operating-system: macos-latest
+          python-version: '3.12'
+
+        - operating-system: ubuntu-latest
+          python-version: '3.12'
+          
+        - operating-system: ubuntu-latest
+          python-version: '3.11'
+          
+        - operating-system: ubuntu-latest
+          python-version: '3.10'
 
     steps:
     - uses: actions/checkout@v4