Improve type for CreationContextFactory::alwaysValidate

[sanfair]

Improve type for \Spatie\LaravelData\Support\Creation\CreationContextFactory::alwaysValidate() function

Without explicitly returning $this type, the current definition loses generic information.
https://phpstan.org/r/1b074136-57c7-4f4e-a2ec-34fd1e9bfd91

  $factory = MentionableRecord::factory()->alwaysValidate();
  \PHPStan\dumpType($factory);

Current state

Dumped type: Spatie\LaravelData\Support\Creation\CreationContextFactory

After the change

Dumped type: Spatie\LaravelData\Support\Creation\CreationContextFactory<App\Dto\MentionableRecord>

[rubenvanassche]

Thanks!