Issue #3403814 by Grimreaper, pdureau: Add label context in themes.

ui_suite_bootstrap.ui_skins.themes.yml

@@ -2,10 +2,12 @@
 # No value because same as plugin ID.
 dark:
   label: "Dark"
+  label_context: "color"
   key: "data-bs-theme"
 
 # No target because scopable.
 # No value because same as plugin ID.
 light:
   label: "Light"
+  label_context: "color"
   key: "data-bs-theme"