Fix sidekiq memory killer warning message

lib/gitlab/sidekiq_middleware/memory_killer.rb

@@ -84,7 +84,7 @@ module Gitlab
       end
       def warn(message, signal: nil)
-        Sidekiq.logger.warn(class: worker.class, pid: pid, signal: signal, message: message)
+        Sidekiq.logger.warn(class: worker.class.name, pid: pid, signal: signal, message: message)
       end
     end
   end

spec/lib/gitlab/sidekiq_middleware/memory_killer_spec.rb

@@ -4,7 +4,7 @@ describe Gitlab::SidekiqMiddleware::MemoryKiller do
   subject { described_class.new }
   let(:pid) { 999 }
-  let(:worker) { double(:worker, class: 'TestWorker') }
+  let(:worker) { double(:worker, class: ProjectCacheWorker) }
   let(:job) { { 'jid' => 123 } }
   let(:queue) { 'test_queue' }
@@ -46,7 +46,10 @@ describe Gitlab::SidekiqMiddleware::MemoryKiller do
       expect(Process).to receive(:kill).with('SIGKILL', pid).ordered
       expect(Sidekiq.logger)
-        .to receive(:warn).with(class: 'TestWorker', message: anything, pid: pid, signal: anything).at_least(:once)
+          .to receive(:warn).with(class: 'ProjectCacheWorker',
+                                  message: anything,
+                                  pid: pid,
+                                  signal: anything).at_least(:once)
       run
     end