Add groupBy method to phpdoc

[DAGpro]

Fix psalm errors if groupBy() is called before or without calling buildQuery()

$this->select()
    ->groupBy('[email protected]_id')
    ->groupBy('label')
    ->buildQuery()
    ->columns(['label', 'count(*) count']);

[roxblnfk]

Hello.

At first glance, your change seems valid: Select proxies methods into Query Builder, including groupBy.

However, from the ORM's perspective, this is not normal usage. Calling Select::groupBy without going down to the lower level (to Query Builder) can disrupt the ORM's logic. This method is intentionally hidden from use in ORM.

That's why I cant apply the changes.