ast.parse allows parenthesised context managers with old feature_version

[hauntsaninja]

The following should raise SyntaxError:

ast.parse('with (CtxManager() as example): ...', feature_version=(3, 9))

[pablogsal]

Thanks for the issue @hauntsaninja

Although we made it official in 3.10, it works on 3.9. Tools supporting 3.9 don't need to support this, but I don't see the advantage in marking it as invalid and being that strict, specially since 3.9 is now in security fixes only

[hauntsaninja]

Thanks, updated the PR to check 3.9 instead of 3.10