fix(ui): fix some cases of stale highlight definitions

fixes #20695

src/nvim/highlight_group.c

@@ -2073,6 +2073,8 @@ void highlight_changed(void)
     }
   }
   highlight_ga.ga_len = hlcnt;
+
+  decor_provider_invalidate_hl();
 }
 
 /// Handle command line completion for :highlight command.