Subprocess timeout causes output to be returned as bytes in text mode

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-03-08.05:41:46.323>
labels = ['3.8', 'type-bug', 'library', '3.9', '3.10']
title = 'Subprocess timeout causes output to be returned as bytes in text mode'
updated_at = <Date 2021-03-30.18:57:45.244>
user = 'https://bugs.python.org/macdjord'

bugs.python.org fields:

activity = <Date 2021-03-30.18:57:45.244>
actor = 'eryksun'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2021-03-08.05:41:46.323>
creator = 'macdjord'
dependencies = []
files = ['49856']
hgrepos = []
issue_num = 43431
keywords = []
message_count = 3.0
messages = ['388257', '388265', '388272']
nosy_count = 3.0
nosy_names = ['giampaolo.rodola', 'eryksun', 'macdjord']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue43431'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']