workflows: Add automatic weekly unit-test container refresh
workflows: Add automatic weekly unit-test container refresh

This will make sure that we don't keep a  broken and un-upgradeable
unit-tests container around, like in the last year.

Closes #14900

cockpit-project/cockpit,garrett/cockpit,mvollmer/cockpit,garrett/cockpit,garrett/cockpit,garrett/cockpit,cockpit-project/cockpit,deryni/cockpit,mvollmer/cockpit,deryni/cockpit,martinpitt/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,deryni/cockpit,cockpit-project/cockpit,garrett/cockpit,martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit,deryni/cockpit,cockpit-project/cockpit,martinpitt/cockpit,deryni/cockpit,deryni/cockpit,martinpitt/cockpit,deryni/cockpit