Kiota regression for discriminator mapping

### What are you generating using Kiota, clients or plugins?

API Client/SDK

### In what context or format are you using Kiota?

Source Build

### Client library/SDK language

None

### Describe the bug

Discovered an issue when generating the Microsoft Graph V1.0 client library. The Kiota generated client library has added a breaking change that is not described by either a CSDL or OpenApi based change (unless missed, need to double check).

The issues are in https://github.com/microsoftgraph/msgraph-sdk-dotnet/pull/3074. The issue is in Applications/Delta/GetDeltaResponse where the return type has been changed from Application to its base DirectoryObject.

Built Kiota, generated, and diff for these scenarios:
- [x] v1.30.0
- [x] main
- [x] mmainer/fixDiscriminator ([PR](https://github.com/microsoft/kiota/pull/7507))
- [ ] pre v1.30.0 (todo)

Looking at the results of (v1.30.0 --> main) `sdvdiff 6ccf6da832742181cba0ab02588c5795b2185e13 80bbd97a29fdac9f5c71694d712c85d946a9a117` may indicate that the cause is from the discriminator mapping.

### Expected behavior

The generated client library uses the correct return type for the Appication getDeltaResponse

### How to reproduce

Need to still repro

### Open API description file

_No response_

### Kiota Version

v1.30.0

### Latest Kiota version known to work for scenario above?(Not required)

TBD

### Known Workarounds

_No response_

### Configuration

_No response_

### Debug output

Click to expand log
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### Other information

_No response_

Start by comparing the v1.30.0 and main generated Microsoft Graph V1.0 clients, focusing on Applications/Delta/GetDeltaResponse and the discriminator mapping changes noted in the sdvdiff command. Reproduce the generation scenario and compare it with PR 7507; done means the generated response uses Application rather than DirectoryObject without an undocumented schema change.

Written by the indexing model from the issue text.