Indeed, reverting commit 41d5b94af44e34ac05d4cd57460ed104ccf96628 makes it work with both parsers:
~/github/python/master master*
❯ ./python -X oldparser
Python 3.9.0a6+ (heads/master-dirty:84724dd239, Apr 29 2020, 20:29:53)
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> norm=lambda m: m+(m and(m[-1]!='\n'and'\n'or'')or'\n')
>>>
~/github/python/master master*
❯ ./python
Python 3.9.0a6+ (heads/master-dirty:84724dd239, Apr 29 2020, 20:29:53)
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> norm=lambda m: m+(m and(m[-1]!='\n'and'\n'or'')or'\n')
>>>