Unable to detect disks suitable for backup when backing up VM with network based disks

**Version used**
virtnbdbackup 2.38
ceph 19.2.3

**Describe the bug**
Unable to detect disks suitable for backup when backing up VM with RBD (ceph) based disks

**Expected behavior**
Backup should proceed

**Hypervisor and/or virtual machine information:**
- OS: Rocky 9.6
- HV type Libvirt 10.10/KVM
- virsh dumpxml for VM:

**Logfiles:**
virtnbdbackup --start-domain -U 'qemu+ssh://root@testsystem1-1/system' --nbd-ip 'testsystem1-1' --nbd-port '29714' --ssh-user 'root' --checkpointdir '/virtnbdbackup/machines/backups/6b9f10d7-09a7-4275-8766-f69605bb08ce/_checkpoints' -d 'baseos-mtwcgtvs' -l 'auto' -o '/virtnbdbackup/machines/backups/6b9f10d7-09a7-4275-8766-f69605bb08ce/2025-10/11a5894d-5d4f-4aa8-9f74-81573882c0ea' -e --raw

[2025-10-21 19:19:07] INFO lib common - printVersion [main]: Version: 2.38 Arguments: /usr/bin/virtnbdbackup --start-domain -U qemu+ssh://root@testsystem1-1/system --nbd-ip testsystem1-1 --nbd-port 29714 --ssh-user root --checkpointdir /virtnbdbackup/machines/backups/6b9f10d7-09a7-4275-8766-f69605bb08ce/_checkpoints -d baseos-mtwcgtvs -l auto -o /virtnbdbackup/machines/backups/6b9f10d7-09a7-4275-8766-f69605bb08ce/2025-10/11a5894d-5d4f-4aa8-9f74-81573882c0ea -e --raw
[2025-10-21 19:19:07] INFO root virtnbdbackup - main [main]: Backup level: [auto]
[2025-10-21 19:19:07] INFO root virtnbdbackup - main [main]: Store checkpoints in: [/virtnbdbackup/machines/backups/6b9f10d7-09a7-4275-8766-f69605bb08ce/_checkpoints]
[2025-10-21 19:19:07] INFO virt client - _connect [main]: Connected to remote host: [testsystem1-1]
[2025-10-21 19:19:07] INFO root virtnbdbackup - main [main]: Libvirt library version: [10010000]
[2025-10-21 19:19:07] INFO root virtnbdbackup - main [main]: NBD library version: [1.20.3]
[2025-10-21 19:19:07] INFO root check - targetDir [main]: Backup mode auto, target folder is empty: executing full backup.
[2025-10-21 19:19:07] ERROR virt client - getDomainDisks [main]: Unable to detect disk volume type for disk [vda] [2025-10-21 19:19:07] WARNING root virtnbdbackup - main [main]: Emulated TPM device attached: User action required. [2025-10-21 19:19:07] WARNING root virtnbdbackup - main [main]: Please manually backup contents of: [/var/lib/libvirt/swtpm/11a5894d-5d4f-4aa8-9f74-81573882c0ea/]
[2025-10-21 19:19:07] INFO root virtnbdbackup - main [main]: Only raw disks attached, switching to backup mode copy.
[2025-10-21 19:19:07] ERROR root virtnbdbackup - main [main]: Unable to detect disks suitable for backup.
[2025-10-21 19:19:07] INFO root metadata - backupConfig [main]: Saving VM config to: [/virtnbdbackup/machines/backups/6b9f10d7-09a7-4275-8766-f69605bb08ce/2025-10/11a5894d-5d4f-4aa8-9f74-81573882c0ea/vmconfig.copy.xml]
[2025-10-21 19:19:07] INFO root metadata - backupBootConfig [main]: Save additional boot config [loader] to: [/virtnbdbackup/machines/backups/6b9f10d7-09a7-4275-8766-f69605bb08ce/2025-10/11a5894d-5d4f-4aa8-9f74-81573882c0ea/OVMF_CODE.secboot.fd]
[2025-10-21 19:19:07] INFO root metadata - backupBootConfig [main]: Save additional boot config [nvram] to: [/virtnbdbackup/machines/backups/6b9f10d7-09a7-4275-8766-f69605bb08ce/2025-10/11a5894d-5d4f-4aa8-9f74-81573882c0ea/baseos-mtwcgtvs_VARS.fd]

**Workaround:**
None found.