refactor(github): build GraphQL query without the client bundle

The eightpoints/guzzle-bundle and idci/graphql-client-bundle only
existed to build one near-static query string, and the bundle's own
HTTP transport was already bypassed in favor of Symfony HttpClient.
Build the query with sprintf/json_encode instead, drop both bundles
from config/bundles.php, and update the test double accordingly.

config/bundles.php

@@ -3,6 +3,4 @@
 return [
     Symfony\Bundle\FrameworkBundle\FrameworkBundle::class => ['all' => true],
     Symfony\Bundle\MonologBundle\MonologBundle::class => ['all' => true],
-    EightPoints\Bundle\GuzzleBundle\EightPointsGuzzleBundle::class => ['all' => true],
-    IDCI\Bundle\GraphQLClientBundle\IDCIGraphQLClientBundle::class => ['all' => true],
 ];