Update jquery-ui-rails from 5.0.5 to 6.0.1.

This was requested to be compatible with the version Debian uses. I'm opening this primarily to see what (if any) tests fail and how hard it'd be to fix it.

Changelog: https://github.com/jquery-ui-rails/jquery-ui-rails/blob/3bc41f13b4611e8445ca885dc5016bf6c3454a8f/History.md#601

Changelog for jQuery UI: https://jqueryui.com/upgrade-guide/1.12/

Fixes #25302 (moved).