Do error when for variable conflicts with a variable in scope

modules/gdscript/gdscript_parser.cpp

@@ -1748,6 +1748,10 @@ GDScriptParser::ForNode *GDScriptParser::parse_for() {
 
 	SuiteNode *suite = alloc_node<SuiteNode>();
 	if (n_for->variable) {
+		const SuiteNode::Local &local = current_suite->get_local(n_for->variable->name);
+		if (local.type != SuiteNode::Local::UNDEFINED) {
+			push_error(vformat(R"(There is already a %s named "%s" declared in this scope.)", local.get_name(), n_for->variable->name), n_for->variable);
+		}
 		suite->add_local(SuiteNode::Local(n_for->variable, current_function));
 	}
 	suite->parent_for = n_for;

modules/gdscript/tests/scripts/parser/errors/variable_conflicts_for_variable.gd

@@ -0,0 +1,4 @@
+func test():
+	var TEST = 1
+	for TEST in 2:
+		pass

modules/gdscript/tests/scripts/parser/errors/variable_conflicts_for_variable.out

@@ -0,0 +1,2 @@
+GDTEST_PARSER_ERROR
+There is already a variable named "TEST" declared in this scope.

modules/gdscript/tests/scripts/parser/errors/variable_conflicts_variable.gd

@@ -0,0 +1,3 @@
+func test():
+	var TEST = 1
+	var TEST = 2

modules/gdscript/tests/scripts/parser/errors/variable_conflicts_variable.out

@@ -0,0 +1,2 @@
+GDTEST_PARSER_ERROR
+There is already a variable named "TEST" declared in this scope.