ci: fix silk-shipit private.yml
ci: fix silk-shipit private.yml

* Also don't print out our service account keys on error

Co-authored-by: Tim Downey <ac5faf2072a7e8487ec8b27348636434d5c3410d@pivotal.io>

cloudfoundry-incubator/cf-networking-release,cloudfoundry-incubator/cf-networking-release,cloudfoundry-incubator/cf-networking-release,cloudfoundry-incubator/cf-networking-release