Apply suggested fix to src/bosh-nats-sync/spec/nats_sync/users_sync_spec.rb from Copilot Autofix

Co-authored-by: Copilot Autofix powered by AI <223894421+github-code-quality[bot]@users.noreply.github.com>

Author: rkoster

src/bosh-nats-sync/spec/nats_sync/users_sync_spec.rb

@@ -35,6 +35,18 @@ module NATSSync
     let(:client_id) { 'client_id' }
     let(:client_secret) { 'client_secret' }
     let(:ca_cert) { 'ca_cert' }
+    let(:sample_director_subject) do
+      file = Tempfile.new('director_subject')
+      file.write(director_subject)
+      file.flush
+      file.path
+    end
+    let(:sample_hm_subject) do
+      file = Tempfile.new('hm_subject')
+      file.write(hm_subject)
+      file.flush
+      file.path
+    end
     let(:director_subject_file) { sample_director_subject }
     let(:hm_subject_file) { sample_hm_subject }
     let(:director_subject) { 'C=USA, O=Cloud Foundry, CN=default.director.bosh-internal' }