Fix new translation is missing the relation id for saving

[Tofandel]

If we do

$tr = $model->translateOrNew('en');
$tr->some_field = 'abc';
$tr->save();

We get a query exception (Field ..._id doesn't have a default value) because the package is not setting the relation key

This PR fixes the issue

[Gummibeer]

Thanks for the improvement. The translation model was never meant to be saved standalone but be saved through the main model. But as it's a very simple fix I'm happy to merge it in.

[Gummibeer]

https://github.com/Astrotomic/laravel-translatable/releases/tag/v11.14.1