containers/unit-tests: Put back sassc
containers/unit-tests: Put back sassc

This was dropped prematurely in commit 012483503e53, our rhel-8.4 branch
still uses it and backporting the sass changes is too intrusive for a
stable branch.

mvollmer/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit