Have zipapp respect SOURCE_DATE_EPOCH

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-10-02.00:10:31.637>
labels = ['type-feature', 'library', '3.11']
title = 'Have zipapp respect SOURCE_DATE_EPOCH'
updated_at = <Date 2021-10-02.00:10:31.637>
user = 'https://github.com/bign8'

bugs.python.org fields:

activity = <Date 2021-10-02.00:10:31.637>
actor = 'bign8'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2021-10-02.00:10:31.637>
creator = 'bign8'
dependencies = []
files = ['50320']
hgrepos = []
issue_num = 45344
keywords = ['patch']
message_count = 1.0
messages = ['403041']
nosy_count = 1.0
nosy_names = ['bign8']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue45344'
versions = ['Python 3.11']