User migration creates a second birthday calendar that can't be removed

Steps to reproduce

1. Use User Migration app to export calendars from a Nextcloud instance
2. Important the file in a new user on a fresh Nextcloud instance
3. Observe that there are now two Birthday calendars; one disappears when turning off the birthday calendar, but the other (migrated-contact_birthdays) stays, and does not sync with new contacts
4. Press Delete on the calendar, it gets struck through, but on a page refresh it is back

Expected behavior

The Birthdays calendar probably shouldn't be migrated at all. It seems like the newly generated Birthdays calendar works perfectly with my migrated contacts.

Actual behavior

I now have two birthday calendars (I'm guessing I can remove the other with an OCC command or similar, but I still feel this can be improved by not migrating it at all, or allowing it to be removed

Calendar app version

6.5.3

CalDAV-clients used

Thunderbird, DAVx5

Browser

Firefox 153

Client operating system

Ubuntu

Server operating system

Debian 13

Web server

Apache

Database engine version

No response

PHP engine version

No response

Nextcloud version

Nextcloud Hub 26

Updated from an older installed version or fresh install

No response

List of activated apps

Nextcloud configuration

Web server error log

Log file

Browser log

Additional info

No response

Start by reproducing the export and import sequence with the User Migration app, then inspect how the migrated contact_birthdays calendar is handled. Done means the migration no longer creates a duplicate Birthday calendar, or the migrated calendar can be deleted and stays removed after a refresh.