ci: allow subclassing any for mypy to enable subclassing Symbol

.github/workflows/python-static-ci.yml

@@ -14,7 +14,7 @@ jobs:
       - uses: python/[email protected]
         with:
           paths: "./src"
-      - run: pip install .[test] && python -m mypy --strict --install-types --non-interactive ./src ./tests ./example
+      - run: pip install .[test] && python -m mypy --strict --install-types --allow-subclassing-any --non-interactive ./src ./tests ./example
 
   audit:
     runs-on: ubuntu-latest