[http-client-java] mgmt, expandable enumMember as property default value isn't working as expected

### Describe the bug

```typespec
union SkuFamily {
string,
A: "A",
}

model Sku {
skuFamily: SkuFamily.A
}
```

Will result in compilation failure.

### Reproduction

Example above.

### Checklist

- [x] Follow our [Code of Conduct](https://github.com/microsoft/typespec/blob/main/CODE_OF_CONDUCT.md)
- [x] Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
- [x] Check that this is a concrete bug. For Q&A open a [GitHub Discussion](https://github.com/Microsoft/typespec/discussions).
- [x] The provided reproduction is a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) of the bug.