xz: Add missing RISC-V on the filter list in the man page

[ivq]

Pull request checklist

• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been reviewed and added / updated if needed (for bug fixes / features)
• [ ] Build was run locally and without warnings or errors
• [ ] All previous and new tests pass

Pull request type

Please check the type of change your PR introduces:

• [ ] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, renaming, typo fix)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [x] Documentation content changes
• [ ] Other (please describe):

What is the current behavior?

The RISC-V filter option should be listed in the man page but not.

What is the new behavior?

List the RISC-V filter.

Does this introduce a breaking change?

• [ ] Yes
• [x] No

Other information

The translation is not handled yet. Currently running po4a/update-po upon commit 5d8d915ebe2e345820a0f54d1baf8d7d4824c0c7 generates changes of over 455 lines and I'm sure sure if they are really needed. Plus, I'm not familiar with the po4a tools so help is needed.

[JiaT75]

Thanks for the PR! This was indeed forgotten. There is no need to worry about the translations. Those are handled by the Translation Project.

I don't think anything else is needed for this PR, so when you are satisfied with the PR you can mark it Ready for review :)