Add furo as a python dependency in the python job of the tests workflow

.github/workflows/tests.yml

@@ -89,7 +89,7 @@ jobs:
       - uses: actions/setup-python@v2
         with:
           python-version: "3.10"
-      - run: pip install --upgrade maturin sphinx
+      - run: pip install --upgrade maturin sphinx furo
       - run: maturin sdist -m python/Cargo.toml
       - run: pip install target/wheels/*.tar.gz
       - run: python -m unittest