add more git-email perl dependencies
    
    There were a few dependencies missing prior to the change in git-2.33
    which Ondřej fixed in the previous commit.
    
    Of the few dependencies being added, only Email::Address and
    Sys::Hostname weren't already pulled in by other dependencies when
    installing git-email.  They each have fallback options, so they aren't
    critical to the function of the application.  (We could use Recommends
    here, if we wanted -- though neither pull in any additional packages at
    this time.)