os.ftruncate on Windows should be sparse

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-03-09.11:19:49.115>
labels = ['3.8', 'library', '3.9']
title = 'os.ftruncate on Windows should be sparse'
updated_at = <Date 2020-03-09.11:19:49.115>
user = 'https://github.com/Artoria2e5'

bugs.python.org fields:

activity = <Date 2020-03-09.11:19:49.115>
actor = 'Artoria2e5'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-03-09.11:19:49.115>
creator = 'Artoria2e5'
dependencies = []
files = []
hgrepos = []
issue_num = 39910
keywords = []
message_count = 1.0
messages = ['363717']
nosy_count = 2.0
nosy_names = ['steve.dower', 'Artoria2e5']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue39910'
versions = ['Python 3.8', 'Python 3.9']