Ignore php8_native_union_with_self test for the moment

Seee php/php-src#18373

Author: thekid

src/test/php/lang/unittest/TypeUnionTest.class.php

@@ -13,7 +13,7 @@
   Nullable
 };
 use test\verify\Runtime;
-use test\{Action, Assert, Expect, Test, Values};
+use test\{Assert, Expect, Ignore, Test, Values};
 
 class TypeUnionTest {
 
@@ -242,7 +242,7 @@ public function php8_native_nullable_union_return_type_name() {
     Assert::equals('?', typeof($f)->getMethod('fixture')->getReturnTypeName()[0]);
   }
 
-  #[Test, Runtime(php: '>=8.0.0-dev')]
+  #[Test, Runtime(php: '>=8.0.0-dev'), Ignore('https://github.com/php/php-src/issues/18373')]
   public function php8_native_union_with_self() {
     $t= typeof(eval('
       namespace lang\unittest;