Fix misprint in tests

Author: a-melnikov

tests/ExpressionLanguage/TestCase.php

@@ -112,7 +112,7 @@ protected function createGraphQLServices(array $services = []): GraphQLServices
         $locateableServices = [
             'typeResolver' => fn () => $this->createMock(TypeResolver::class),
             'queryResolver' => fn () => $this->createMock(TypeResolver::class),
-            'mutationResolver' => fn () => $$this->createMock(MutationResolver::class),
+            'mutationResolver' => fn () => $this->createMock(MutationResolver::class),
         ];
 
         foreach ($services as $id => $service) {