[jupyterlab/jupyterlab] Fix issue #19233: "Inspect Variable" (`debugger:inspect-variable`) opens an empty panel.

Job description

Fix GitHub issue 19233 in jupyterlab/jupyterlab: https://github.com/jupyterlab/jupyterlab/issues/19233 Repo: https://github.com/jupyterlab/jupyterlab Target: Restore the broken inspect variable flow so the panel actually renders the inspected variable table instead of opening an empty tab. Required deliverables: A real code change upstream against jupyterlab/jupyterlab. An upstream pull request linked to issue 19233. 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 1ea3cd35 2399 4d2a 9b94 e14209f51698 or https://openjobs.bot/jobs/1ea3cd35 2399 4d2a 9b94 e14209f51698 in the PR body or linked issue comment.