Add tests to CI

.github/workflows/tests.yaml

@@ -0,0 +1,19 @@
+name: tests
+
+on: [push]
+
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python: ['3.9', '3.10', '3.11', '3.12']
+
+    steps:
+    - uses: actions/checkout@v4
+    - uses: actions/setup-python@v5
+      with:
+        python-version: ${{ matrix.python }}
+        allow-prereleases: true
+    - run: python -m pip install tox
+    - run: tox -e py