[9.x] Fix clone issue on updateOrCreate and firstOrCreate

[deefour]

#42087 breaks functionality on BelongsToMany with a custom pivot table/model for updateOrCreate() and firstOrCreate().

The current behavior,

$instance = $this->clone()->where($attributes)->first()

is creating an issue in which all columns from the pivot table are applied to $instance. This isn't expected behavior in general, but is a breaking change introduced in #42087 when the pivot table has a primary key matching the source model - $instance->id will end up being the id from the pivot table, not the target table the firstOrCreate() or updateOrCreate() is pointing to.

The chain of magic __call and __clone methods between Relation, Eloquent\Builder and Query\Builder is a bit hard to follow. This is compounded by the fact that $this->clone() uses the ForwardsCalls trait to delegate the call into Eloquent\Builder, returning an instance of that builder instead of a copy of `Relation.

(clone $this) - directly cloning the Relation to do the $instance query keeps the pivot table data out of $instance.

/cc @trideout