[#4744] Bump test zipkin version (#4755)
[#4744] Bump test zipkin version (#4755)

- The current zipkin version is ~2 yrs old

Signed-off-by: Sameer Vohra <f4f210ea33849b94e7dd9c4c6983b40037b50a5b@vmware.com>
knative/eventing,knative/eventing