broken help is shown if the signature of lambda has return_annotation

gistfile1.txt

$ python
Python 3.8.2 (default, Mar  2 2020, 00:44:41)
[Clang 11.0.0 (clang-1100.0.33.17)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> foo = lambda x = 1: 1
>>> help(foo)
Help on function <lambda> in module __main__:

<lambda> lambda x=1
>>> import inspect
>>> foo.__signature__ = inspect.signature(foo)
>>> help(foo)
Help on function <lambda> in module __main__:

<lambda> lambda x=1
>>> foo.__signature__ = inspect.signature(foo).replace(return_annotation=int)
>>> help(foo)
Help on function <lambda> in module __main__:

<lambda> lambda x=1) -> in