getSetMapping(): Return value must be of type bool, array returned

This patch resolves a TypeError in Quicktabs::getSetMapping() by changing the return type from bool to array, ensuring it accurately reflects the actual return value ($this->setMapping), which is always an array; this prevents runtime error which was occuring by type mismatch, enforces strict type safety as required in PHP 7+ and PHP 8+
Hence, Moving the state of the issue to RTBC.

Thanks for catching that, I have committed the code.