Bump traefik-k8s channel to latest/beta

Loadbalancer IPs on traefik services are
not retained on restart. This is fixed in
traefik-k8s latest/beta [1][2].
Bump the traefik-k8s default channel to
latest/beta

[1] canonical/traefik-k8s-operator#381
[2] canonical/observability-libs#104

sunbeam-python/sunbeam/versions.py

@@ -20,7 +20,7 @@
 OPENSTACK_CHANNEL = "2024.1/stable"
 OVN_CHANNEL = "24.03/stable"
 RABBITMQ_CHANNEL = "3.12/stable"
-TRAEFIK_CHANNEL = "latest/stable"
+TRAEFIK_CHANNEL = "latest/beta"
 MICROCEPH_CHANNEL = "reef/candidate"
 SUNBEAM_MACHINE_CHANNEL = "2024.1/stable"
 SUNBEAM_CLUSTERD_CHANNEL = "2024.1/stable"