containers: Skip libssh security update in unit-tests container
containers: Skip libssh security update in unit-tests container

The security update broke keyboard-interactive authentication, see
https://bugs.debian.org/913870. Until this is fixed, use the released
version.

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