Add contains_char() for single-character 'contains' calls.

modules/gdscript/gdscript_parser.cpp

@@ -4323,7 +4323,7 @@ bool GDScriptParser::export_annotations(AnnotationNode *p_annotation, Node *p_ta
 				push_error(vformat(R"(Argument %d of annotation "%s" is empty.)", i + 1, p_annotation->name), p_annotation->arguments[i]);
 				return false;
 			}
-			if (arg_string.contains(",")) {
+			if (arg_string.contains_char(',')) {
 				push_error(vformat(R"(Argument %d of annotation "%s" contains a comma. Use separate arguments instead.)", i + 1, p_annotation->name), p_annotation->arguments[i]);
 				return false;
 			}