Run Python unittests in workflow

.github/workflows/main.yml

@@ -29,3 +29,18 @@ jobs:
       - name: Run pylint
         run: pylint --ignore=test_mwmatching.py python tests
 
+  # Run unittests on multiple Python versions.
+  unittest-python:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.7", "3.8", "3.9", "3.10", "3.11", "3.12-dev"]
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v4
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Run unittests
+        run: python3 python/test_mwmatching.py
+