docs: reorder all MIGRATION.md sections newest-first - #51

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02, oven-sh/setup-bun@735343b667d3e6f658f44d0eca948eb6282f2b76. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/