`mark-pinned` but for locked issues

Description

We have locked-issue that adds a label to the individual issue's header. This feature would instead add a lock icon or marker to the lists

• The code most likely looks like mark-merge-commits-in-list
• Style probably like mark-pinned, without highlight. TBD

See https://github.com/refined-github/refined-github/pull/9663 for more info on what doesn't work (namely an icon before the title).

Alternative could also be a (locked) pill style on the list but it would not be that noticeable.

Example URLs

https://github.com/refined-github/refined-github/issues?q=generated%20is%3Apr%20sort%3Acomments-asc