Add a GitHub Action to run pytest

Author: cclauss

.github/workflows/ci.yml

@@ -0,0 +1,8 @@
+name: ci
+on: [pull_request, push]
+jobs:
+  pytest:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+      - run: pipx run pytest --doctest-modules