Make CITestStreamFilter compatible with php_user_filter

[paulbalandan]

Description
Related to #4883

During inheritance of php_user_filter: Uncaught ErrorException: Return type of CodeIgniter\Test\Filters\CITestStreamFilter::filter($in, $out, &$consumed, $closing) should either be compatible with php_user_filter::filter($in, $out, &$consumed, bool $closing): int, or the #[ReturnTypeWillChange] attribute should be used to temporarily suppress the notice

Checklist:

• Securely signed commits