fix: obtain libvirtversion instead of hypervisor version

[anokfireball]

The LibVirtVersion currently (incorrectly) reports the Hypervisor version. Identical behaviour between CHV and QEMU.

> kubectl get hypervisors.kvm.cloud.sap node008-bb088 -o yaml | yq ".status.libVirtVersion"
50.0.0

> ssh 10.245.239.62
root@10.245.239.62's password:
  ____               _              _     _
 / ___| __ _ _ __ __| | ___ _ __   | |    _ _ __  _   ___  __
| |  _ / _` | '__/ _` |/ _ \ '_ \  | |   | | '_ \| | | \ \/ /
| |_| | (_| | | | (_| |  __/ | | | | |___| | | | | |_| |>  <
 \____|\__,_|_|  \__,_|\___|_| |_| |_____|_|_| |_|\__,_/_/\_\
Garden Linux 1877.10.3 (based on Debian GNU/Linux trixie)

Welcome to node008-bb088  Mon Feb 16 15:47:41 UTC 2026
[...]

root@node008-bb088:~$ virsh version
Compiled against library: libvirt 11.10.0
Compiled with the Cloud Hypervisor patches by Cyberus Technology for SAP/Apeiro
|-Commit: be575f7b06806e84aec56bf531e7029a1d44dd01
Using library: libvirt 11.10.0
Using API: CH 11.10.0
Running hypervisor: CH 50.0.0

[github-actions]

Merging this branch will not change overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/cobaltcore-dev/kvm-node-agent/internal/libvirt	40.00% (ø)

---

Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/cobaltcore-dev/kvm-node-agent/internal/libvirt/libvirt.go	71.50% (ø)	200	143	57

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.