fix(molecule): select distro-specific private interfaces

- Use eth1 for Ubuntu and Debian Bento guests when present.
- Keep enp0s8 for Rocky Linux guests and other images.
- Apply the selection consistently across all Molecule scenarios.

molecule/ipv6/overrides.yml

@@ -6,12 +6,12 @@
       ansible.builtin.set_fact:
         # See:
         # https://github.com/flannel-io/flannel/blob/67d603aaf45ef80f5dd39f43714fc5e6f8a637eb/Documentation/troubleshooting.md#Vagrant
-        flannel_iface: enp0s8
+        flannel_iface: "{{ 'eth1' if 'eth1' in ansible_facts.interfaces else 'enp0s8' }}"
 
         # In this scenario, we have multiple interfaces that the VIP could be
         # broadcasted on. Since we have assigned a dedicated private network
         # here, let's make sure that it is used.
-        kube_vip_iface: enp0s8
+        kube_vip_iface: "{{ 'eth1' if 'eth1' in ansible_facts.interfaces else 'enp0s8' }}"
 
         # The test VMs might be a bit slow, so we give them more time to join the cluster:
         retry_count: 45