test_mailbox: Duplicate keys in _sample_headers cause _check_sample to only test one value

[The-Compiler]

Bug report

A sample of mail headers is used in tests here:

cpython/Lib/test/test_mailbox.py

Lines 34 to 35 in b2694ab

	for key, value in _sample_headers.items():
	self.assertIn(value, msg.get_all(key))

However, _sample_headers is defined as a dict, despite having duplicate keys, such as Received:

cpython/Lib/test/test_mailbox.py

Lines 2267 to 2290 in b2694ab

	_sample_headers = {
	"Return-Path":"<gkj@gregorykjohnson.com>",
	"X-Original-To":"gkj+person@localhost",
	"Delivered-To":"gkj+person@localhost",
	"Received":"""from localhost (localhost [127.0.0.1])
	by andy.gregorykjohnson.com (Postfix) with ESMTP id 356ED9DD17
	for <gkj+person@localhost>; Wed, 13 Jul 2005 17:23:16 -0400 (EDT)""",
	"Delivered-To":"gkj@sundance.gregorykjohnson.com",
	"Received":"""from localhost [127.0.0.1]
	by localhost with POP3 (fetchmail-6.2.5)
	for gkj+person@localhost (single-drop); Wed, 13 Jul 2005 17:23:16 -0400 (EDT)""",
	"Received":"""from andy.gregorykjohnson.com (andy.gregorykjohnson.com [64.32.235.228])
	by sundance.gregorykjohnson.com (Postfix) with ESMTP id 5B056316746
	for <gkj@gregorykjohnson.com>; Wed, 13 Jul 2005 17:23:11 -0400 (EDT)""",
	"Received":"""by andy.gregorykjohnson.com (Postfix, from userid 1000)
	id 490CD9DD17; Wed, 13 Jul 2005 17:23:11 -0400 (EDT)""",
	"Date":"Wed, 13 Jul 2005 17:23:11 -0400",
	"From":""""Gregory K. Johnson" <gkj@gregorykjohnson.com>""",
	"To":"gkj@gregorykjohnson.com",
	"Subject":"Sample message",
	"Mime-Version":"1.0",
	"Content-Type":"""multipart/mixed; boundary="NMuMz9nt05w80d4+\"""",
	"Content-Disposition":"inline",
	"User-Agent": "Mutt/1.5.9i" }

causing those tests to only check one of those values. It should probably be a list of tuples instead? If this is indeed unintended, I'd be happy to open a PR.

cc @warsaw

(Found by running flake8 over Lib/ out of curiosity, see #93010 (comment))

Your environment

• CPython versions tested on: Seems to be around since ~forever, added to the git repo in 477c8d5.
• Operating system and architecture: Archlinux x86_64

• PR: gh-93121: fix test_mailbox where some test cases were accidentally dropped #93242