Check to see if `HEAD` is the same as what we have locally. If it is:
don't bother to `git fetch`.
ClosesHomebrew/homebrew#47888.
ClosesHomebrew/homebrew#49219.
Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>
Also, rename the existing updater to `update-ruby` to allow using as
a fallback. It will eventually be removed.
ClosesHomebrew/homebrew#49109.
Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>