Fix race condition with `created` event

Anyway, there is no point in creating a registry during
`checksum_succeeded` event since verification will not proceed for a
registry that is not yet synced.

ee/app/models/concerns/geo/verifiable_replicator.rb

@@ -182,6 +182,7 @@ module Geo
     # Called by Gitlab::Geo::Replicator#consume
     def consume_event_checksum_succeeded(**params)
       return unless Gitlab::Geo.secondary?
+      return unless registry.persisted?
 
       registry.verification_pending!
     end

ee/spec/support/shared_examples/models/concerns/verifiable_replicator_shared_examples.rb

@@ -457,10 +457,15 @@ RSpec.shared_examples 'a verifiable replicator' do
       end
 
       context 'on a Geo secondary' do
+        before do
+          stub_secondary_node
+        end
+
+        context 'with a persisted registry' do
           let(:registry) { replicator.registry }
 
           before do
-          stub_secondary_node
+            registry.save!
           end
 
           context 'with a registry which is verified' do
@@ -487,6 +492,15 @@ RSpec.shared_examples 'a verifiable replicator' do
             end
           end
         end
+
+        context 'with an unpersisted registry' do
+          it 'does not persist the registry' do
+            replicator.consume_event_checksum_succeeded
+
+            expect(replicator.registry.persisted?).to be_falsey
+          end
+        end
+      end
     end
   end