ci(actions): generate egg_info

Generate the egg_info before executing the tests otherwise setup.py
doesn't register the correct version of the test suite, but possibly
the older version already available in nixpkgs.

.github/workflows/nix.yml

@@ -23,6 +23,7 @@ jobs:
         with:
           path: /run/user/${{ env.UID }}/http_cache.sqlite
           key: ${{ runner.os }}-http_cache.sqlite
+      - run: nix develop --command bash -c "python setup.py egg_info"
       - run: nix develop --command bash -c "python setup.py test"
       - run: nix develop --command bash -c "py.test --nbval --nbval-sanitize-with examples/sanitize.cfg examples/index.ipynb"
       - uses: actions/cache/save@v3