http.client not allowing non-ascii in headers

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-08-28.21:04:14.111>
labels = ['3.8', 'library']
title = 'http.client not allowing non-ascii in headers'
updated_at = <Date 2020-08-29.14:45:16.137>
user = 'https://bugs.python.org/yellalena'

bugs.python.org fields:

activity = <Date 2020-08-29.14:45:16.137>
actor = 'yellalena'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-08-28.21:04:14.111>
creator = 'yellalena'
dependencies = []
files = []
hgrepos = []
issue_num = 41658
keywords = []
message_count = 3.0
messages = ['376047', '376060', '376066']
nosy_count = 2.0
nosy_names = ['xtreak', 'yellalena']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue41658'
versions = ['Python 3.8']