Change StringName -> String conversion from operator String() to string().

modules/gdscript/editor/gdscript_highlighter.cpp

@@ -947,7 +947,7 @@ void GDScriptSyntaxHighlighter::_update_cache() {
 			HashMap<StringName, Variant> scr_constant_list;
 			scr_class->get_constants(&scr_constant_list);
 			for (const KeyValue<StringName, Variant> &E : scr_constant_list) {
-				member_keywords[E.key.operator String()] = member_variable_color;
+				member_keywords[E.key.string()] = member_variable_color;
 			}
 			scr_class = scr_class->get_base_script();
 		}