shodowed var warning for `for` loop counter

Fix: #39268
(cherry picked from commit 54835a530210c9620973a63dd30ff1d6bbe43a96)

modules/gdscript/gdscript_parser.cpp

@@ -3120,6 +3120,13 @@ 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
 
 				BlockNode *check_block = p_block;
 				while (check_block) {