overriding model property with more specific object type doesn't work #1123

Describe the bug
When an object schema derives from another object schema using allOf, and redeclares a property that had an object type to use a different object type, the generated code uses the old type for that property.

OpenAPI Spec File
https://gist.github.com/eli-bl/d5658d6714e1c9ef544ef1fc8902960a

With this example, the type of SpecialTask.result in the generated code should be SpecialTaskOutputData. Instead it is being declared as BaseTaskResult, the same as BaseTask.result.

Desktop (please complete the following information):

• OS: macOS 14.5
• Python Version: 3.8.15
• openapi-python-client version: 0.21.5