Add return type for generator returning never

Author: muglug

Zend/tests/return_types/never_generator.phpt

@@ -0,0 +1,12 @@
+--TEST--
+never return type: not valid as a parameter type
+--FILE--
+<?php
+
+function generateList(string $uri): never {
+    yield 1;
+    exit();
+}
+?>
+--EXPECTF--
+Fatal error: Generator return type must be a supertype of Generator, never given in %s on line %d