test: add pytest coverage and run tests in CI

.gitea/workflows/build-and-publish.yaml

@@ -40,7 +40,16 @@ jobs:
           # Full history and tags are required to derive the next version
           # from the conventional-commit messages since the last release.
           fetch-depth: 0
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: 3.12
 
+      - name: Install test dependencies
+        run: python -m pip install --upgrade pip && pip install -r requirements.txt
+
+      - name: Run unit tests
+        run: pytest -q
       - name: Determine registry host
         run: echo "REGISTRY=${GITHUB_SERVER_URL#*://}" >> "$GITHUB_ENV"