Increase number of messages published in this test

spec/stress/concurrent_consumers_stress_spec.rb

@@ -21,7 +21,7 @@ def any_not_drained?(qs)
       let(:colors) { ["red", "blue", "white"] }
 
       let(:n) { 32 }
-      let(:m) { 1000 }
+      let(:m) { 5000 }
 
       it "successfully drain all queues" do
         ch0  = @connection.create_channel