vTPM on KVM does not persist data (ACS 4.20.1.0, Ubuntu 24.04)

>### problem

after a shutdown, the /var/lib/libvirt/swtpm/ which holds the tpm data is gone. When starting the vm again, the folder is re-created with empty tpm files.

I am using a similar tpm definition in manually configured kvm guests, if those vm are powered off the folder remains.

### versions

4.20.1.0
Ubuntu 24.04

### The steps to reproduce the bug

```
root@VM-647bf7bc-bdca-48fa-8329-8b7a103f9ab6:~# echo "Hello, TPM!" > datafile
root@VM-647bf7bc-bdca-48fa-8329-8b7a103f9ab6:~# tpm2_nvwrite -C o -i datafile 0x1500016
root@VM-647bf7bc-bdca-48fa-8329-8b7a103f9ab6:~# tpm2_nvread -C o 0x1500016
WARN: Reading full size of the NV index
Hello, TPM!
```

Instance power cycle, and tryi to read our value again from the tpm

```
root@VM-647bf7bc-bdca-48fa-8329-8b7a103f9ab6:~# tpm2_nvread -C o 0x1500016
WARN: Reading full size of the NV index
WARNING:esys:src/tss2-esys/api/Esys_NV_ReadPublic.c:309:Esys_NV_ReadPublic_Finish() Received TPM Error
ERROR:esys:src/tss2-esys/esys_tr.c:243:Esys_TR_FromTPMPublic_Finish() Error NV_ReadPublic ErrorCode (0x0000018b)
ERROR:esys:src/tss2-esys/esys_tr.c:398:Esys_TR_FromTPMPublic() Error TR FromTPMPublic ErrorCode (0x0000018b)
ERROR: Esys_TR_FromTPMPublic(0x18B) - tpm:handle(1):the handle is not correct for the use
ERROR: Unable to run tpm2_nvread
root@VM-647bf7bc-bdca-48fa-8329-8b7a103f9ab6:
```

### What to do about it?

_No response_

Commencez par reproduire la séquence de power-cycle sur Ubuntu 24.04 et inspectez la manière dont le répertoire /var/lib/libvirt/swtpm/ est géré lorsque la VM s’arrête. C’est terminé lorsque la valeur NV du TPM reste lisible après le redémarrage et que le répertoire n’est pas recréé avec des fichiers TPM vides.

Rédigé par le modèle d'indexation à partir du texte de l'issue.