Add tests for python client with disallowAdditionalPropertiesIfNotPresent set to true

[wing328]

Add tests for python client with disallowAdditionalPropertiesIfNotPresent set to true

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[multani]

@wing328 Before merging this, and once #16867 has been merged (I'm not sure which one goes first), could you also add this new sample to https://github.com/OpenAPITools/openapi-generator/blob/master/.github/workflows/samples-python-client-echo-api.yaml?

[wing328]

added via 6d692ae