Continue support for taskwarrior 2.x as well as 3.x

### Describe your improvement idea or feature request

Taskwarrior development towards 3.x is great, but many of us are still going to be using task 2.x because of database changes, regressions, etc., so I am hoping that taskwarrior-flutter development and testing does not leave the 2.x branch behind. Thanks

### How would you like to see it implemented?

continued testing on the 2.x AND 3.x branches

### Put here any screenshots or videos (optional)

_No response_

### How can we contact you (optional)

_No response_

### Would you like to work on this issue?

None

### By submitting this issue, I have confirmed that:

- [X] I have starred the repo ⭐ and watched 👀 it on GitHub and followed the contribution guidelines.

この issue にはファイル、テスト、エントリポイントが記載されていません。まずアプリの Taskwarrior 統合と既存のテストまたは CI 設定を特定し、次に Taskwarrior 2.x と 3.x の両方をどのように実行して検証できるかを判断してください。継続的なテストで両方のブランチをカバーし、モバイルアプリを壊さなければ完了です。

索引モデルが issue の本文から書いたものです。