In dark mode, you cannot see the icon for setting the badges for sitelinks.
This is because the badge is set as a background-image (SVG) in `jquery.wikibase.sitelinkview.less` and has a `#000` fill colour.
**Steps to reproduce:**
- Open an item in dark mode, e.g. https://www.wikidata.org/wiki/Q4115189?useskin=vector-2022&vectornightmode=1
- Start editing the sitelinks
- Notice that next to each sitelink title there’s an invisible, but clickable badge button (the cursor will change to a different cursor); clicking that will open the badge selector as usual
**Acceptance criteria:**
- [] The badge icon is visible in both light and dark mode
**Notes:**
See e.g. [this change](https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/1079986/14/view/resources/jquery/wikibase/toolbar/themes/default/jquery.wikibase.toolbarbutton.less) for how we fixed this for other icons by turning them into masks.