Close the advisory lock connection manually

When recreating the DB in migration tests, there may be connections
remaining from ActiveRecord::AdvisoryLockBase

spec/support/database_cleaner.rb

@@ -35,6 +35,8 @@ RSpec.configure do |config|
       puts "Recreating the database"
       start = Gitlab::Metrics::System.monotonic_time
 
+      ActiveRecord::AdvisoryLockBase.clear_all_connections!
+
       ActiveRecord::Tasks::DatabaseTasks.drop_current
       ActiveRecord::Tasks::DatabaseTasks.create_current
       ActiveRecord::Tasks::DatabaseTasks.load_schema_current