[3.11] gh-114211: Update EmailMessage doc about ordered keys (GH-114224) (#114226)

Ordered keys are no longer unlike 'real dict's.
(cherry picked from commit 8cda72037b262772399b2b7fc36dee9340d74fd6)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

Miss Islington (bot) committed 2y ago

4ec2e2eeee44267bc65af2a2f505ef4dcc60365e

Parent: 2dca689

Committed by GitHub <noreply@github.com> on 1/18/2024, 2:56:03 AM