stubgen does not support debug f-strings using python 3.9+

[rvaquerizor]

Bug Report

I get an error like the following whenever a debug f-string is used in my code and I try to generate a stub to by used with mypy:

Critical error during semantic analysis: myfile.py:76: error: f-string: self documenting expressions are only supported in Python 3.8 and greater

To Reproduce

1. Put a debug string in your code, like the following:

option = 3
print(f'Debug print: {option=}')

2. execute stubgen on it, and it will complain with the above error message

Expected Behavior

Debug f-strings supported by stubgen, as long as py3.8+ is used.

Actual Behavior

stubgen fails to generate the pyi file when debug f-strings are found in the py module.

Your Environment

• Mypy version used: 0.812
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.9 and 3.10
• Operating system and version: Ubuntu, 5.11.0-37-generic Refactor code into packages #41-Ubuntu SMP x86_64 x86_64 x86_64 GNU/Linux

[JelleZijlstra]

Duplicate of #10905