Filament repeater test bug

Setup and reproduction

cp .env.example .env
touch database/database.sqlite
composer install
php artisan migrate:fresh --seed
php artisan test

Issue description

When testing resources that use the Repeater component, the fillForm method, due to its approach of deep-filling data one value at a time, will create invalid states that do not occur in normal use. In this repro, the itemLabel callback has an assumption that $state is pre-loaded with the keys corresponding to the repeater items' schema, with each key's value initialized to null when nothing has been set yet. This assumption is valid when rendering the form normally, but is not correct when in the test environment using the test helpers, causing errors.

Expected: The livewire test helper and its fillForm method should initialize form state for tests in a fashion identical to normal form rendering.

// From the resource:
->itemLabel(function (array $state): ?string {
    if (! $state['author'] || ! $state['title']) {
        return null;
    }

    return "{$state['author']}: {$state['title']}";
})

// This fails due to an absent 'title' key in $state
it('populates multiple fields in schema', function () {
    livewire(CreateArticle::class)
        ->fillForm(['quotes' => [[
            'author' => 'Sally',
            'title' => 'Foo',
            'body' => 'Bar',
        ]]])
        ->call('create')
        ->assertHasNoFormErrors();
});