`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