Use a more succinct syntax to count by queues

`tally` is introduced since Ruby 2.7 and also adds small performance
gain compared to the old approach (~ 1.6x).

lib/gitlab/sidekiq_cluster.rb

@@ -111,7 +111,7 @@ module Gitlab
     end
 
     def self.count_by_queue(queues)
-      queues.each_with_object(Hash.new(0)) { |element, hash| hash[element] += 1 }
+      queues.tally
     end
 
     def self.proc_details(counts)

spec/lib/gitlab/sidekiq_cluster_spec.rb

@@ -123,6 +123,14 @@ RSpec.describe Gitlab::SidekiqCluster do
     end
   end
 
+  describe '.count_by_queue' do
+    it 'tallies the queue counts' do
+      queues = [%w(foo), %w(bar baz), %w(foo)]
+
+      expect(described_class.count_by_queue(queues)).to eq(%w(foo) => 2, %w(bar baz) => 1)
+    end
+  end
+
   describe '.concurrency' do
     using RSpec::Parameterized::TableSyntax