[Python Guidelines] Model parameters are still documented as accepting dict-like inputs

Bad code snippet:
```Python
geometry: Geometry,
```

What it should do:
The current Python guideline says parameters typed as model instances should also accept dict-like inputs, but this is now out of date for generated code in azure-planetarycomputer. The generated signature is expected to type the parameter as the model type only, not as a union with `Mapping`.

Good code snippet:
```Python
geometry: Geometry,
```