[BUG] MSI Swagger, invalid definition of `readOnly`

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### API Spec link

https://github.com/Azure/azure-rest-api-specs/blob/84f223e8bea800a1a0b503b8c28675abf91f92a2/specification/msi/resource-manager/Microsoft.ManagedIdentity/stable/2024-11-30/ManagedIdentity.json#L541-L546

### API Spec version

all versions

### Describe the bug

### Context
`readOnly` on `properties` of `Identity` and `IdentityUpdate` is invalid in 2 senses:
#### 1. `readOnly` alongside `$ref` is not supported in OpenAPI 2.0/3.0

Previously M4 will ignore this kind of definition.

#### 2. In reality, some of the properties in the `properties` are settable, the `properties` itself therefore shouldn't be defined as `readOnly`
`IsolationScope` in `UserAssignedIdentityProperties` is settable:

### Issue
Though in Swagger, `Identity`'s `properties` is defined as `readOnly`(which means not settable):
https://github.com/Azure/azure-rest-api-specs/blob/84f223e8bea800a1a0b503b8c28675abf91f92a2/specification/msi/resource-manager/Microsoft.ManagedIdentity/stable/2024-11-30/ManagedIdentity.json#L539-L547

IMHO, it shouldn't be `readOnly`.

### Expected behavior

`Identity`'s `properties` shouldn't be defined as `readOnly`.

### Actual behavior

https://github.com/Azure/azure-rest-api-specs/blob/84f223e8bea800a1a0b503b8c28675abf91f92a2/specification/msi/resource-manager/Microsoft.ManagedIdentity/stable/2024-11-30/ManagedIdentity.json#L539-L547

### Reproduction Steps

N/A

### Environment

_No response_

Start with specification/msi/resource-manager/Microsoft.ManagedIdentity/stable/2024-11-30/ManagedIdentity.json around lines 539-547, then check the other API versions referenced by the issue. Verify the definitions of Identity and IdentityUpdate and remove the invalid readOnly declaration from properties where appropriate; done means the specifications validate and settable properties remain usable.

Written by the indexing model from the issue text.