Enable frozen string for spec/lib/gitlab/graphql

Partially addresses:

https://gitlab.com/gitlab-org/gitlab/issues/27703

spec/lib/gitlab/graphql/authorize/authorize_resource_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Gitlab::Graphql::Authorize::AuthorizeResource do

spec/lib/gitlab/graphql/loaders/batch_lfs_oid_loader_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Gitlab::Graphql::Loaders::BatchLfsOidLoader do

spec/lib/gitlab/graphql/loaders/batch_model_loader_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Gitlab::Graphql::Loaders::BatchModelLoader do