"email.message.Message.as_bytes": fails to correctly handle "charset"

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-07-15.19:18:03.191>
labels = ['type-bug', 'expert-email', '3.9']
title = '"email.message.Message.as_bytes":  fails to correctly handle "charset"'
updated_at = <Date 2020-07-15.20:40:58.721>
user = 'https://github.com/d-maurer'

bugs.python.org fields:

activity = <Date 2020-07-15.20:40:58.721>
actor = 'dmaurer'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['email']
creation = <Date 2020-07-15.19:18:03.191>
creator = 'dmaurer'
dependencies = []
files = []
hgrepos = []
issue_num = 41307
keywords = []
message_count = 2.0
messages = ['373711', '373724']
nosy_count = 3.0
nosy_names = ['barry', 'dmaurer', 'r.david.murray']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue41307'
versions = ['Python 3.9']