GDScript: Fix typing of iterator in for loop

modules/gdscript/tests/scripts/analyzer/features/for_loop_on_variant.gd

@@ -0,0 +1,15 @@
+func test():
+	var variant_int: Variant = 1
+	var weak_int = 1
+
+	for x in variant_int:
+		if x is String:
+			print('never')
+		print(x)
+
+	for x in weak_int:
+		if x is String:
+			print('never')
+		print(x)
+
+	print('ok')

modules/gdscript/tests/scripts/analyzer/features/for_loop_on_variant.out

@@ -0,0 +1,4 @@
+GDTEST_OK
+0
+0
+ok