Set site id explicitly to avoid drift

[mraerino]

No description provided.

[github-actions]

🏗️ Terraform Plan

Terraform used the selected providers to generate the following execution
plan. Resource actions are indicated with the following symbols:
  ~ update in-place

Terraform will perform the following actions:

  # module.supernode[0].netbox_virtual_machine.supernode will be updated in-place
  ~ resource "netbox_virtual_machine" "supernode" {
      ~ custom_fields = {
          - "proxmox_vm_id" = "" -> null
        }
        id            = "59"
        name          = "supernode-dev-0"
        tags          = []
        # (12 unchanged attributes hidden)
    }

  # module.supernode[1].netbox_virtual_machine.supernode will be updated in-place
  ~ resource "netbox_virtual_machine" "supernode" {
      ~ custom_fields = {
          - "proxmox_vm_id" = "" -> null
        }
        id            = "60"
        name          = "supernode-dev-1"
        tags          = []
        # (12 unchanged attributes hidden)
    }

Plan: 0 to add, 2 to change, 0 to destroy.