version resilient model could not handle nested discriminators

[tadelesh]

For current cadl-ranch test case: https://github.com/Azure/cadl-ranch/blob/main/packages/cadl-ranch-specs/http/type/model/inheritance/nested-discriminator/main.tsp, the deserialization for the nested discriminator will be wrong.
For example, when we call test.partner.sharktype, we will get error.

test = Salmon(
{
        "age": 1,
        "kind": "salmon",
        "partner": {
            "age": 2,
            "kind": "shark",
            "sharktype": "saw",
        }
})