Perform Replicator#verify even if not "started"

* `Geo::VerificationWorker` is already deduplicated for identical args
  since it is marked `idempotent!`
* When `verification_state` is not `verification_started`, it is not
  necessary for `VerificationWorker#perform` or `Replicator#verify` to
  exit without doing work. Furthermore, it is unexpected.

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

@@ -126,8 +126,7 @@ module Geo
     # Calculates checksum and asks the model/registry to update verification
     # state.
     def verify
-      # Deduplicate verification job
-      return unless model_record.verification_started?
+      model_record.verification_started! unless model_record.verification_started?
 
       calculation_started_at = Time.current
       checksum = model_record.calculate_checksum

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

@@ -299,37 +299,23 @@ RSpec.shared_examples 'a verifiable replicator' do
         stub_primary_node
       end
 
-      context 'when verification was started' do
-        before do
-          model_record.verification_started!
-        end
-
-        context 'when the checksum succeeds' do
-          it 'delegates checksum calculation and the state change to model_record' do
-            expect(model_record).to receive(:calculate_checksum).and_return('abc123')
-            expect(model_record).to receive(:verification_succeeded_with_checksum!).with('abc123', kind_of(Time))
+      context 'when the checksum succeeds' do
+        it 'delegates checksum calculation and the state change to model_record' do
+          expect(model_record).to receive(:calculate_checksum).and_return('abc123')
+          expect(model_record).to receive(:verification_succeeded_with_checksum!).with('abc123', kind_of(Time))
 
-            replicator.verify
-          end
+          replicator.verify
         end
+      end
 
-        context 'when an error is raised during calculate_checksum' do
-          it 'passes the error message' do
-            error = StandardError.new('Some exception')
-            allow(model_record).to receive(:calculate_checksum) do
-              raise error
-            end
-
-            expect(model_record).to receive(:verification_failed_with_message!).with('Error calculating the checksum', error)
-
-            replicator.verify
+      context 'when an error is raised during calculate_checksum' do
+        it 'passes the error message' do
+          error = StandardError.new('Some exception')
+          allow(model_record).to receive(:calculate_checksum) do
+            raise error
           end
-        end
-      end
 
-      context 'when verification was not started' do
-        it 'does not call calculate_checksum!' do
-          expect(model_record).not_to receive(:calculate_checksum)
+          expect(model_record).to receive(:verification_failed_with_message!).with('Error calculating the checksum', error)
 
           replicator.verify
         end