updating test workflow

.github/workflows/tests.yml

@@ -14,10 +14,10 @@ jobs:
       with:
         submodules: recursive
 
-    - name: Set up Python 3.9
+    - name: Set up Python 3.12
       uses: actions/setup-python@v2
       with:
-        python-version: 3.9
+        python-version: 3.12
 
     - name: Install MPI
       run: |
@@ -28,6 +28,7 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip install pytest pytest-cov pytest-mock
+        pip install coverage
         pip install coveralls
         pip install -r requirements.txt