Fix accidental creation of js/ directory under site-packages/ when installing Plotly

[emilykl]

Link to issue

Closes #5584

Description of change

Fixes issue since Plotly 6.7.0, introduced by #5540, where pip install plotly would unintentionally create a js/ directory under site-packages/, interfering with any other package which might use the js/ name.

Demo

N/A

Testing strategy

To reproduce the issue:

1. Create a fresh Python virtual environment
2. Run pip install plotly==6.7.0 (or uv pip install ...)
3. Notice that the following directory exists: $VENV_ROOT/lib/pythonX.Y/site-packages/js

To verify that this PR fixes the issue:

1. Check out this branch
2. Run python -m build from the root folder, and make sure it runs without error

• Verify that new dist/plotly-6.7.0.tar.gz and dist/plotly-6.7.0-py3-none-any.whl files are created

4. Create a fresh Python virtual environment
5. Run pip install dist/plotly-6.7.0-py3-none-any.whl
6. Verify that $VENV_ROOT/lib/pythonX.Y/site-packages/js DOES NOT exist
7. Verify that $VENV_ROOT/share/jupyter/labextensions/jupyterlab-plotly/install.json DOES exist
8. To test installing the tar file, repeat steps 4-7 replacing the .whl file path with the .tar.gz file path

Guidelines

• I have reviewed the pull request guidelines and the Code of Conduct and confirm that this PR follows them.
• I have added an entry to the changelog if needed (not required for documentation PRs).

[mgorny]

Thank you!