Make announce and archive jobs independent of CI cache
The CI cache is not guaranteed to work or exist and runners will continue even if the cache is not available.
Currently, we rely on the cache as a base to diff the xeplist.xml against. In the worst case, this will cause emails not to be sent and attic entries not to be created.
None of this cannot be fixed after the event, but to have the pipeline stable, we need to find another solution.
One option would be to require merge commits on main
and diff the commit which is being built against its first parent if the cache is absent && (the pipeline is not triggered || an override environment variable was set). Using this only as a fallback also reduces the impact in the case where a non-merge commit is at the HEAD.