Add codecov action

Author: browniebroke

.github/workflows/test.yml

@@ -34,3 +34,6 @@ jobs:
           python-version: ${{ matrix.python-version }}
       - run: python -m pip install tox
       - run: tox -f py$(echo ${{ matrix.python-version }} | tr -d .)
+      - uses: codecov/codecov-action@v4
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}