ci: Sync bootc-ubuntu-setup action from bootc-dev/infra

ci: Sync bootc-ubuntu-setup action from bootc-dev/infra

The CI was failing because we were pulling podman/crun/skopeo
from Debian testing which has become unreliable. The bootc-dev/infra
repository maintains a reusable action that uses Ubuntu's plucky
repository instead, which is more appropriate for ubuntu-24.04 runners.

This also brings in additional improvements from the shared action:
- Disk space cleanup on the runner
- Unprivileged /dev/kvm access setup
- Optional libvirt stack support

Assisted-by: ClaudeCode (Claude Opus 4.5)