fix: enable closure once test again

Author: TorstenDittmann

tests/src/integration/closure.php

@@ -6,7 +6,7 @@
 assert(test_closure()('works') === 'works');
 
 // Closure once
-// $closure = test_closure_once('test');
+$closure = test_closure_once('test');
 
-// assert(call_user_func($closure) === 'test');
-// assert_exception_thrown($closure);
+assert(call_user_func($closure) === 'test');
+assert_exception_thrown($closure);