Include sha256 hashes of release downloads in announcement communications

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-12-15.01:40:48.306>
labels = ['deferred-blocker', '3.9', '3.10', '3.11']
title = 'Include sha256 hashes of release downloads in announcement communications'
updated_at = <Date 2021-12-15.08:49:37.120>
user = 'https://github.com/gpshead'

bugs.python.org fields:

activity = <Date 2021-12-15.08:49:37.120>
actor = 'ydroneaud'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2021-12-15.01:40:48.306>
creator = 'gregory.p.smith'
dependencies = []
files = []
hgrepos = []
issue_num = 46077
keywords = []
message_count = 1.0
messages = ['408579']
nosy_count = 2.0
nosy_names = ['gregory.p.smith', 'ydroneaud']
pr_nums = []
priority = 'deferred blocker'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue46077'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']