az kusto cluster update with --sku specified updates unrelated properties

### Describe the bug

When running `az kusto cluster update --name --subscription <sub>--resource-group --sku name="" tier="Standard"` to migrate compute skus, several unrelated properties of the cluster also were updated.</sub>

1. enableAutoStop switched from `false` to `true`
2. enableDiskEncryption switched from `true` to `false`
3. enablePurge switched from `true` to `false`

This is quite unexpected since these properties were not specified, and I do not see anything in the command docs that they are required or have default values.

### Related command

`az kusto cluster update`

### Errors

n/a

### Issue script & Debug output

n/a - appears to reproduce with any invocation that involves a sku migration.

### Expected behavior

I expect the SKU to be updated, but those unconfigured properties to retain their original values.

### Environment Summary

azure-cli 2.87.0 *

core 2.87.0 *
telemetry 1.1.0

Extensions:
acr-transfer Unknown
acrtransfer 1.1.0
aks-preview 18.0.0b43
azure-devops 1.0.2
azure-firewall 1.2.2
kusto 0.5.0
nsp 1.0.0
resource-graph 2.1.0
support 2.0.1

Dependencies:
msal 1.36.0
azure-mgmt-resource 24.0.0

Python location '/bin/python3.12'
Config directory '/home//.azure'
Extensions directory '/home//.azure/cliextensions'
Extensions system directory '/usr/lib/python3.12/site-packages/azure-cli-extensions'

Python (Linux) 3.12.9 (main, Jun 2 2026, 15:06:48) [GCC 13.2.0]

Legal docs and information: aka.ms/AzureCliLegal

### Additional context

_No response_