Enable mypy lint in CI

.github/workflows/lint.yml

@@ -28,3 +28,21 @@ jobs:
         with:
           version: ${{ steps.version.outputs.version }}
           args: format --diff
+
+  mypy:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+          cache: pip
+
+      - name: Install dependencies
+        run: pip install -r requirements-txt.txt
+
+      # Allow untyped calls for older Python versions
+      - name: Run mypy
+        run: mypy