Consider adding `devtools::check_mac_release()` to the release issue checklist

[jennybc]

Definitely needs to wait a while, for the new macOS builder (https://mac.r-project.org/macbuilder/submit.html) to accumulate some usage.

Even then, it's not completely clear we (tidyverse) want or need this, given that we mostly develop on macOS and, increasingly, on M1.

It could be an item we only add to the checklist if there's a src/ directory.