staticimport checks should error in rc-v* branches

[gadenbuie]

It's easy to miss the staticimport checks since you have to look at a PR in just the right way to find them. That makes sense for normal day-to-day checks, but I think it's worth considering making it an error in the rc- branch so that we don't forget to update them.

The checks as they are now wouldn't trigger an error or message unless a function currently being statically imported was updated, and we usually have a reason for updating those static imports... so we should probably update them before pushing out a new release.

[gadenbuie]

Related: we could also adopt a policy of adding a release bullet to remind us via use_release_issue(). I added this in promises

release_bullets <- function() {
  c(
    "Update staticimports: `staticimports::import()`"
  )
}