spec/initializers/mailer_retries_spec.rb:20 is flaky

Job #1317049365 failed for f16fc45c:

bundle exec rspec spec/lib/marginalia_spec.rb spec/initializers/mailer_retries_spec.rb

Failures:
  1) Mailer retries sets retries for mailers to 3
     Failure/Error: expect(Sidekiq::Queues['mailers'].first).to include('retry' => 3)
       expected nil to include {"retry" => 3}, but it does not respond to `include?`
     # ./spec/initializers/mailer_retries_spec.rb:23:in `block (2 levels) in <top (required)>'
     # ./spec/initializers/mailer_retries_spec.rb:15:in `block (2 levels) in <top (required)>'
     # ./spec/spec_helper.rb:372:in `block (3 levels) in <top (required)>'
     # ./spec/support/sidekiq_middleware.rb:9:in `with_sidekiq_server_middleware'
     # ./spec/spec_helper.rb:363:in `block (2 levels) in <top (required)>'
     # ./spec/spec_helper.rb:359:in `block (3 levels) in <top (required)>'
     # ./lib/gitlab/application_context.rb:31:in `with_raw_context'
     # ./spec/spec_helper.rb:359:in `block (2 levels) in <top (required)>'
Finished in 36 minutes 49 seconds (files took 56.97 seconds to load)
4041 examples, 1 failure, 21 pending
Failed examples:
rspec ./spec/initializers/mailer_retries_spec.rb:20 # Mailer retries sets retries for mailers to 3