fix(ci): set boot order to disk-first to prevent install loop

OVMF was rebooting back into the installer CD after PVE install completed.
Setting boot_order to scsi0 first means the first boot falls through to
CD (empty disk), and after install OVMF boots from the EFI entry on disk.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/infrastructure/main.tf

@@ -29,8 +29,9 @@ resource "proxmox_virtual_environment_vm" "nested_pve" {
   node_name = var.target_node
   vm_id     = var.vm_id
 
-  machine = "q35"
-  bios    = "ovmf"
+  machine    = "q35"
+  bios       = "ovmf"
+  boot_order = ["scsi0", "ide2"]
 
   cpu {
     type    = "host"