Duplicated task doesn't have check list from original

[raggesilver]

Describe the bug Duplicating a task doesn't duplicate it's checklist.

To Reproduce Steps to reproduce the behavior:

1. Create a task with some checklist items
2. Duplicate the task you just created
3. Checklist doesn't exist in the duplicated task

Expected behavior The checklist from the original task should be copied over to the duplicated one.

Desktop (please complete the following information):

• OS or DE: Fedora 33 / Gnome 3.38
• Version: Flatpak 2.5.3

          ID: com.github.alainm23.planner
         Ref: app/com.github.alainm23.planner/x86_64/stable
        Arch: x86_64
      Branch: stable
     Version: 2.5.3
     License: GPL-3.0+
      Origin: flathub
  Collection: org.flathub.Stable
Installation: system
   Installed: 107.0 MB
     Runtime: org.gnome.Platform/x86_64/3.36
         Sdk: org.gnome.Sdk/x86_64/3.36