This commit reduces the cron schedule for nightly builds down from
hourly and to actually nightly (at ~3am).
The push-to-master flow now triggers effectively the same thing at push
time, so if anything, this will reduce the latency of the continuous
package build and deploy.
The push-to-master flow will now skip builds if it changes only the
docs.
The mac builds started to fail with a crate resolution issue that I
can't reproduce locally shortly after I updated the cache action. Let's
tweak the cache key to see if that clears things up.
