chore: Update flutter_pty dependency to fix Windows script issue

[Lutra-Fs]

Pull Request Details

What issue does this PR address

• This PR fix the issue which pacman cannot be installed on Windows Rattle by switching the flutter-pty upstream to KitasaitamalBlues's one. See this PR Fixed the incorrect environment variable when creating a process under Windows TerminalStudio/flutter_pty#15 for details. Once this PR gets merged, we could switch back to the main repo.

• Closes [Windows] failed to install pacman in RattleNG R Console #268

Checklist

Complete the check-list below to ensure your branch is ready for PR.

Flutter Style Guide: https://survivor.togaware.com/gnulinux/flutter-style.html

• Screenshots included in linked issue
• Changes adhere to the style and coding guideline
• No confidential information
• No duplicated content
• No lint check errors related to your changes (make prep or flutter analyze lib)
• Pre-exisiting lint errors noted:
  warning - Unused import: 'package:rattle/r/start.dart' - lib\app.dart:36:8 - unused_import
  warning - The value of the local variable 'stdout' isn't used - lib\features\visual\display.dart:53:12 - unused_local_variable
• Tested on at least one device
  • Android Phone
  • Android Emulator
  • Chrome on Android
  • Chrome
  • iOS
  • Linux
  • MacOS
  • Windows
• Added a reviewer

Finalising

Once PR discussion is complete and reviewer has approved:

• Merge dev into the branch
• Resolve any conflicts
• Add one line summary into CHANGELOG.md
• Bump appropriate version number in pubspec.yaml
• Push to git repository and review
• Merge PR into dev (gjwgit)

[gjwgit]

Thanks.