Not 100% sure this would be considered a bug, but it seems at least worth filing to check. This is a behaviour difference between the new parser and the old one. It's very easy to reproduce:

<mock-chroot> sh-5.0# PYTHONOLDPARSER=1 python3
Python 3.9.0b1 (default, May 29 2020, 00:00:00) 
[GCC 10.1.1 20200507 (Red Hat 10.1.1-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from _ast import *
>>> compile("(*starred)", "<unknown>", "exec", flags=PyCF_ONLY_AST)
<ast.Module object at 0x7fe1504532e0>
>>> 
<mock-chroot> sh-5.0# python3
Python 3.9.0b1 (default, May 29 2020, 00:00:00) 
[GCC 10.1.1 20200507 (Red Hat 10.1.1-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from _ast import *
>>> compile("(*starred)", "<unknown>", "exec", flags=PyCF_ONLY_AST)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<unknown>", line 1
    (*starred)
              ^
SyntaxError: invalid syntax

That is, you can compile() the expression "(*starred)" with PyCF_ONLY_AST flag set with the old parser, but not with the new one. Without PyCF_ONLY_AST you get a SyntaxError with both parsers, though a with the old parser, the error message is "can't use starred expression here", not "invalid syntax".