Bad PHPStan type for `$variables` parameter of `Client::runQuery`

[medunrad]

First of all, thanks for saving this package ❤️

I think that the PHPStan type of parameter $variables of Client::runQuery is not correct. There is type @param array<string,string> $variables, but I think that @param array<string, mixed> $variables suits better.

Look at this GraphQL query:

mutation($checkYoutubeVideoParam: CheckYoutubeVideoParam!) {
  checkYoutubeVideo(checkYoutubeVideoParam: $checkYoutubeVideoParam) {
    message
    success
  }
}

variables:

{
  "checkYoutubeVideoParam":{
    "videoId":"123456"
  }
}

As far as I know, I need to pass an array:

[
  'checkYoutubeVideoParam' => [
    'videoId' => '123456'
  ]
];

which does not suit the type above.

Everything works, but PHPStan is not satisfied.