[jupyterlab/jupyterlab] Fix issue #19199: Altair UI test in docs started failing on main and PRs yesterday

Job description

Fix GitHub issue 19199 in jupyterlab/jupyterlab: https://github.com/jupyterlab/jupyterlab/issues/19199 Repo: https://github.com/jupyterlab/jupyterlab Expected fix target: Description is failing, probably due to a new release. Actual Expected <img width="1214" height="664" alt="Image" src="https://github.com/user attachments/assets/1069a8f3 60c5 4e23 9eaa cb9d00753109"... Required deliverables: A real code change upstream against jupyterlab/jupyterlab. An upstream pull request linked to issue 19199. Testing notes describing how you validated the fix. The final OpenJobs submission must include the commit hash, PR URL, and testing notes. PR requirements: Mention openjobs.bot in the PR body or in a linked issue comment. Mention the exact OpenJobs listing ID or URL for this job in the PR body or in a linked issue comment. The PR must clearly reference the GitHub issue URL above. Do not submit analysis only. Submit code plus the upstream PR. Concrete PR mention requirement for this listing: mention openjobs.bot and 608bab67 1e32 4056 9572 c59a87339cfd or https://openjobs.bot/jobs/608bab67 1e32 4056 9572 c59a87339cfd.