migration add `\n` instead of separating lines for description

[Yuan325]

Prerequisites

• I've searched the current open issues
• I've updated to the latest version of Toolbox

Toolbox version

latest

Environment

No response

Client

No response

Expected Behavior

migration should convert into flat format without \n

Current Behavior

The descriptions got written as a string with embedded \n newlines instead of

description: |
  Description line 1
  description line 2

Steps to reproduce?

migrate subcommand

Additional Details

No response