Error moving task with subtasks from one projet to another

[BPier]

Describe the bug
When moving a tasks that contains subtasks from project A to project B, the parent task and the subtasks are moved in Planify. In Nextcloud only the parent task is moved to project B and the subtasks stay in Project A.

At the next synchronisation the subtask is deleted.

To Reproduce
Steps to reproduce the behavior:

• In Planify, in an instance synchronized with Nexcloud create 2 projects: Project A and Project B
• In Project A, Create a parent task ("Parent") with a subtask ("Child 1")
• Make sure that the tasks are synchronised in Nextcloud
• in Planify move the task "Parent" to project B
  • In Planify -> Now the task "Parent" and the subtask "Child 1" is located in Project B
  • in Nextcloud -> Now the task "Parent" is located in Project B and the task "Child 1" is now alone in Project A
• Click on the wheel to force the synchronisation in Planify
• Now the task Child 1 has been removed from the parent in planify
• From now on the behavior is a bit chaotic, the task might appear or disapear each refresh in nextcloud

Expected behavior
The tasks AND the subtasks should be moved in Planify AND Nextcloud

Desktop (please complete the following information):

• OS or DE: NixOS, KDE Plasma
• Version: NixOS unstable, Nextcloud version 30.0.2 , Planify 4.11.6

[janvlug]

Slightly related to #1457 and #2700.