Make RFC822.MailboxAddress.has_distinct_name is case-insensitive

This prevents mailboxes being marked as spoofed when the name part and
address part are equal but with different case.
5 jobs for wip/email-spoofing-case in 29 minutes and 27 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #338286
fedora

00:04:03

passed #338287
ubuntu

00:08:05

 
  Test
passed #338288
flatpak

00:20:26

 
  Deploy
passed #338289
review

00:00:30

passed #338290
allowed to fail manual
stop_review

00:00:24