Update core.stub

Author: staabm

stubs/core.stub

@@ -335,6 +335,5 @@ function pcntl_signal(int $signal, $handler, bool $restart_syscalls = true): boo
 
 /**
  * @param-later-invoked-callable $callback
- * @return string|array|object|null
  */
-function set_error_handler(?callable $callback, int $error_levels = E_ALL) {}
+function set_error_handler(?callable $callback, int $error_levels = E_ALL): ?callable {}