[5.6] Check UPDATED_AT column existence in HasOneOrMany::update()

[staudenmeir]

Running an update query on an HasOne/HasMany relationship fails if the related model uses timestamps, but doesn't have an UPDATED_AT column:

class Bug extends Eloquent {
    const UPDATED_AT = null;
}

class Foo extends Eloquent {
    public function bugs() {
        return $this->hasMany(Bug::class);
    }
}

$foo->bugs()->update(['test' => 'bar']);

This PR checks whether the UPDATED_AT column exists before updating it.

Fixes #23741.