Update Rouge to v3.21.0

What does this MR do?

Updates rouge to improve syntax highlighting, including some significant unicode-handling improvements

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Closes #220566 (closed)