[Bug Report] "btrbk diff" without "sudo" throws error (backend_local_user=btrfs-progs-sudo)

I added the commands btrfs, readlink, and test to the sudoers file and set backend_local_user=btrfs-progs-sudo. btrbk without sudo should now be possible. However, 'btrbk diff user.20240714T0229 user.20240716T1705' returns:
```
btrbk diff user.20240714T0229 user.20240716T1705
ERROR: Failed to fetch modified files for: /mnt/backup/user.20240716T1705
ERROR: ... Command execution failed (exitcode=1)
ERROR: ... sh: btrfs subvolume find-new '/mnt/backup/user.20240716T1705' 1632
ERROR: ... can't perform the search: Operation not permitted
ERROR: ... can't perform the search: Operation not permitted
```
It is trying to execute `btrfs subvolume find-new '/mnt/backup/user.20240716T1705' 1632`. This command is not appended with `sudo -n` like it should be (backend_local_user=btrfs-progs-sudo). Therefore, the command fails.