bpo-34246: Use no mutable default args in smtplib (GH-8554)


Some methods of the SMTP class use mutable default arguments. Specially
`send_message` is affected as it mutates one of the args by appending items
to it, which has side effects on further calls.
(cherry picked from commit d5fbe9b1a3d65ceeb9159c5ba999ee966a945f76)

Co-authored-by: Pablo Aguiar <scorphus@gmail.com>
diff --git a/Misc/ACKS b/Misc/ACKS
index bcf5604..1c53672 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -22,6 +22,7 @@
 Anton Afanasyev
 Ali Afshar
 Nitika Agarwal
+Pablo S. Blum de Aguiar
 Jim Ahlstrom
 Farhan Ahmad
 Matthew Ahrens