Add new failing test

Author: Girgias

Zend/tests/type_declarations/callable/callable_variance_closure.phpt

@@ -0,0 +1,14 @@
+--TEST--
+Closure should be covariant with callable
+--FILE--
+<?php
+
+class A {
+    public function foo(Closure $c): callable {}
+}
+class B extends A {
+    public function foo(callable $c): Closure {}
+}
+?>
+--EXPECTF--
+Fatal error: Declaration of B::foo(callable $c): Closure must be compatible with A::foo(Closure $c): callable in %s on line %d