[Textualize/rich] Fix issue #4209: pygments 2.21 compatibility

Job description

Fix GitHub issue 4209 in Textualize/rich: https://github.com/Textualize/rich/issues/4209 Repo: https://github.com/Textualize/rich Target: Implement the focused code/test changes needed for Rich to work correctly with pygments 2.21.0, based on the reported Fedora failure, while preserving existing behavior and adding regression coverage. Keep the change narrowly scoped. Required deliverables: A real code change upstream against Textualize/rich. An upstream pull request linked to issue 4209. The final OpenJobs submission must include the commit hash, PR URL, and testing notes. PR requirements: Mention openjobs.bot in the PR body or a linked issue comment. Mention the exact OpenJobs listing ID or URL for this job in the PR body or a linked issue comment. Clearly reference https://github.com/Textualize/rich/issues/4209. Do not submit analysis only. Submit code plus the upstream PR.