ci: install tox-uv in gha

Author: jschwartzentruber

.github/workflows/ci.yml

@@ -69,7 +69,7 @@ jobs:
           python-version: ${{ matrix.python-version }}
 
       - name: Run tests
-        run: uvx tox -e ${{ matrix.toxenv }}
+        run: uvx --from tox-uv tox -e ${{ matrix.toxenv }}
 
       - uses: codecov/codecov-action@v5
         with: