Casts finalized_by migration version to an integer

When the finalized_by key is present in the BBM dictionary file,
the migration version should be cast as an integer, otherwise
ActiveRecord will fail to find the target version, and it will
throw an error.

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/151467#note_1887895592

Changelog: fixed

spec/support/helpers/migrations_helpers.rb

@@ -121,8 +121,10 @@ def previous_migration(steps_back = 2)
   end
 
   def finalized_by_version
-    ::Gitlab::Database::BackgroundMigration::BatchedBackgroundMigrationDictionary
+    finalized_by = ::Gitlab::Database::BackgroundMigration::BatchedBackgroundMigrationDictionary
       .entry(described_class.to_s.demodulize)&.finalized_by
+
+    finalized_by.to_i if finalized_by
   end
 
   def migration_schema_version

spec/support_specs/helpers/migrations_helpers_spec.rb

@@ -107,4 +107,30 @@
       end
     end
   end
+
+  describe '#finalized_by_version' do
+    let(:dictionary_entry) { nil }
+
+    before do
+      allow(helper).to receive(:described_class)
+      allow(::Gitlab::Database::BackgroundMigration::BatchedBackgroundMigrationDictionary).to(
+        receive(:entry).and_return(dictionary_entry)
+      )
+    end
+
+    context 'when no dictionary was found' do
+      it { expect(helper.finalized_by_version).to be_nil }
+    end
+
+    context 'when finalized_by is a string' do
+      let(:dictionary_entry) do
+        instance_double(
+          ::Gitlab::Database::BackgroundMigration::BatchedBackgroundMigrationDictionary::Entry,
+          finalized_by: '20240104155616'
+        )
+      end
+
+      it { expect(helper.finalized_by_version).to eq(20240104155616) }
+    end
+  end
 end