[Microsoft.ManagedIdentity/userAssignedIdentities]: Properties incorrectly flagged as read-only for User Assigned Managed Identities

### Resource Type

Microsoft.ManagedIdentity/userAssignedIdentities

### Api Version

2025-01-31-preview

### Issue Type

Property(s) inaccurately marked read-only/write-only

### Other Notes

When I try to change the properties of my User Assigned Managed Identities (UAMI), I get the following warning:

`The property "properties" is read-only. Expressions cannot be assigned to read-only properties. If this is a resource type definition inaccuracy, report it using https://aka.ms/bicep-type-issues.bicep[BCP073](https://aka.ms/bicep/core-diagnostics#BCP073)`

I know System Assigned Managed Identities (SAMI) are read-only but you _can_ modify UAMI properties. Happens across multiple API versions, not just the one I specified.

### Bicep Repro

```bicep
resource UAMIName 'Microsoft.ManagedIdentity/userAssignedIdentities@2025-01-31-preview' = {
location: 'westus3'
tags: {}
name: 'UAMIName'
properties: {
isolationScope: 'Regional'
}
}
```

### Confirm

- [x] I have read the troubleshooting guide and looked for duplicates.

Reproduce the warning with the supplied Bicep resource using Microsoft.ManagedIdentity/userAssignedIdentities@2025-01-31-preview, then inspect the generated type definition for the properties declaration and compare it with the UAMI API behavior described. Done means the UAMI properties can be assigned without the read-only diagnostic across the affected API versions.

Written by the indexing model from the issue text.