shodowed var warning for `for` loop counter

Fix: #39268

modules/gdscript/gdscript_parser.cpp

@@ -3178,6 +3178,13 @@ void GDScriptParser::_parse_block(BlockNode *p_block, bool p_static) {
 
 				IdentifierNode *id = alloc_node<IdentifierNode>();
 				id->name = tokenizer->get_token_identifier();
+#ifdef DEBUG_ENABLED
+				for (int j = 0; j < current_class->variables.size(); j++) {
+					if (current_class->variables[j].identifier == id->name) {
+						_add_warning(GDScriptWarning::SHADOWED_VARIABLE, id->line, id->name, itos(current_class->variables[j].line));
+					}
+				}
+#endif // DEBUG_ENABLED
 
 				tokenizer->advance();