Incorrect duplicate detection for imported notebooks with sub-notebooks

[MatsG23]

Environment

Joplin version: 2.8.8 (prod, linux) installed from snap Platform: Linux OS specifics: openSUSE Tumbleweed 20220725 (Wayland) + KDE Plasma 5.25.3

Steps to reproduce

1. Export a notebook with sub-notebooks to JEX
2. Change the name of the notebook in the app to prevent a name conflict on import
3. Import the created JEX file again
4. Every sub-notebook gets a "(1)" added behind its name.

Describe what you expected to happen

Since there are no duplicate sub-notebooks names in the newly created notebook, the names should be kept. A number ("(1)", "(2)", ...) must not be added.

[kamalbuilds]

hi @laurent22 @MatsG23 can I work on this issue?