Use with_lock_retries in migration

db/migrate/20200721034536_add_issue_type_to_issues.rb

 # frozen_string_literal: true
 
 class AddIssueTypeToIssues < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
   DOWNTIME = false
 
-  def change
+  def up
     with_lock_retries do
       # Set default to issue type
-      add_column :issues, :issue_type, :integer, limit: 2, default: 0
+      add_column :issues, :issue_type, :integer, limit: 2, default: 0, null: false
+    end
+  end
+
+  def down
+    with_lock_retries do
+      remove_column :issues, :issue_type
     end
   end
 end

db/schema_migrations/20200721034536

+9d30ae6ea32db6cbc5871e214a9c2bf8f1a37fbb586f5e39f6bc2ab58768607b
\ No newline at end of file

db/schema_migrations/20200721043502

+13731676720dd93887dc55374c9052f1087a2e817eb347fd63a19d9398899d75
\ No newline at end of file

db/structure.sql

@@ -12529,6 +12529,7 @@ CREATE TABLE public.issues (
     sprint_id bigint,
     issue_type smallint DEFAULT 0,
     CONSTRAINT check_fba63f706d CHECK ((lock_version IS NOT NULL))
+    issue_type smallint DEFAULT 0 NOT NULL
 );
 
 CREATE SEQUENCE public.issues_id_seq