disable test for `null.nonExistent()` on lua and as3

tests/unit/src/unit/issues/Issue4988.hx

@@ -10,7 +10,9 @@ class Issue4988 extends Test {
 				var d:{i:Null<Int>} = null;
 				value = (d.i > 0);
 				(null:Dynamic).nonExistent();
+				#if !(lua || as3)
 				null.nonExistent();
+				#end
 				t(false);
 			} catch(e:Dynamic) {
 				t(true);