Give the subrequest its own request format. (#705)

Author: Breuls

src/GraphQL/Buffers/SubRequestBuffer.php

@@ -89,6 +89,7 @@ public function resolveBufferArray(array $buffer) {
       $currentRequest->files->all(),
       $currentRequest->server->all()
     );
+    $request->setRequestFormat('_graphql_subrequest');
 
     $request->attributes->set('_graphql_subrequest', function () use ($buffer) {
       return array_map(function ($item) {