bots: Fix ipa refresh image trigger
bots: Fix ipa refresh image trigger

ubuntu-1604 does not exist any more, should be ubuntu-1804.

mvollmer/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,garrett/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,andreasn/cockpit,deryni/cockpit,deryni/cockpit,mvollmer/cockpit,deryni/cockpit,cockpit-project/cockpit,deryni/cockpit,andreasn/cockpit,andreasn/cockpit,cockpituous/cockpit,cockpituous/cockpit,andreasn/cockpit,martinpitt/cockpit,garrett/cockpit,garrett/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpituous/cockpit,garrett/cockpit,andreasn/cockpit,cockpituous/cockpit,andreasn/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,deryni/cockpit,moraleslazaro/cockpit,deryni/cockpit,deryni/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,cockpit-project/cockpit,andreasn/cockpit,garrett/cockpit