Resource icons are added to the fallback icon theme, so they won't
get used if a matching icon is found in the configured theme.
That includes fallback names, so Adwaita's "window-close-symbolic"
takes precedence over "window-close-24-symbolic" in hicolor.
Fix this by using a custom name for a custom icon.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1640>
29e2b15236