Don't allow datetime parsing to accept non-Ascii digits

GitHub fields:

assignee = None
closed_at = <Date 2020-07-17.17:11:22.617>
created_at = <Date 2020-01-09.21:10:55.846>
labels = ['type-security', '3.8', '3.7', 'library', '3.9']
title = "Don't allow datetime parsing to accept non-Ascii digits"
updated_at = <Date 2020-07-17.17:11:22.616>
user = 'https://github.com/cool-RR'

bugs.python.org fields:

activity = <Date 2020-07-17.17:11:22.616>
actor = 'cool-RR'
assignee = 'none'
closed = True
closed_date = <Date 2020-07-17.17:11:22.617>
closer = 'cool-RR'
components = ['Library (Lib)']
creation = <Date 2020-01-09.21:10:55.846>
creator = 'cool-RR'
dependencies = []
files = []
hgrepos = []
issue_num = 39280
keywords = ['patch']
message_count = 10.0
messages = ['359695', '359696', '359697', '359698', '359707', '359715', '359729', '359730', '361123', '361271']
nosy_count = 6.0
nosy_names = ['mark.dickinson', 'vstinner', 'steven.daprano', 'methane', 'cool-RR', 'p-ganssle']
pr_nums = ['17931']
priority = 'normal'
resolution = None
stage = 'resolved'
status = 'closed'
superseder = None
type = 'security'
url = 'https://bugs.python.org/issue39280'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']