IDLE: Wrong highlighting when \n follows def/class

GitHub fields:

assignee = 'https://github.com/terryjreedy'
closed_at = None
created_at = <Date 2020-04-25.03:29:56.860>
labels = ['3.8', 'expert-IDLE', 'type-bug', '3.7', '3.9']
title = 'IDLE: Wrong highlighting when \\n follows def/class'
updated_at = <Date 2020-04-27.00:57:33.373>
user = 'https://github.com/Alex-Python-Programmer'

bugs.python.org fields:

activity = <Date 2020-04-27.00:57:33.373>
actor = 'terry.reedy'
assignee = 'terry.reedy'
closed = False
closed_date = None
closer = None
components = ['IDLE']
creation = <Date 2020-04-25.03:29:56.860>
creator = 'Alex-Python-Programmer'
dependencies = []
files = []
hgrepos = []
issue_num = 40384
keywords = []
message_count = 3.0
messages = ['367249', '367251', '367337']
nosy_count = 2.0
nosy_names = ['terry.reedy', 'Alex-Python-Programmer']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue40384'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']