The CircleCI cache frequently expires and forces a massive rebuild of our dependencies

Since we have no Nix binary cache set up we have to build a huge amount of software just to get to the point where we can run the ZKAPAuthorizer test suite. We have a CircleCI cache set up for these dependencies. Unfortunately CircleCI deletes it after 15 days. Development is not active enough to make sure this cache gets refreshed within that window (which avoids the deletion and the need to rebuild everything).

Run a job on a schedule that refreshes the cache so we only have to rebuild our deps if they actually need rebuild, not just because the cache got dropped.