[python] Fixes endpoint overload type hint + required property not in properties

[spacether]

• Fixes endpoint overload type hint when there is no request body
• Fixes schema required property not in properties use case

Note:
This makes the python client here have the same fixes as the 1.02 release from here:
https://github.com/openapi-json-schema-tools/openapi-json-schema-generator/releases/tag/1.0.2

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