In RawConfigParser "vars: _section" should be "vars: Optional[_section]" #2847

Methods get*() and items() of RawConfigParser and SectionProxy declare argument vars=None.

However in the stubs they're defined as vars: _section, where _section = Mapping[str, str], which effectively creates problems when inheriting from ConfigParser and trying to follow the original defaults pattern.

Probably in all these methods it should be vars: Optional[_section].