[doc] Unintuitive error when using generator expression in class property

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2016-05-04.14:34:32.938>
labels = ['3.11', 'type-bug', '3.9', '3.10', 'docs']
title = '[doc] Unintuitive error when using generator expression in class property'
updated_at = <Date 2021-12-12.00:51:42.440>
user = 'https://github.com/frewsxcv'

bugs.python.org fields:

activity = <Date 2021-12-12.00:51:42.440>
actor = 'iritkatriel'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2016-05-04.14:34:32.938>
creator = 'corey'
dependencies = []
files = []
hgrepos = []
issue_num = 26951
keywords = []
message_count = 5.0
messages = ['264819', '264821', '264830', '264845', '348191']
nosy_count = 7.0
nosy_names = ['mark.dickinson', 'steven.daprano', 'docs@python', 'serhiy.storchaka', 'corey', 'xiang.zhang', 'abarry']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue26951'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']