Allow to delete NSG Flow if subnet has been deleted

### Describe the bug

If a subnet is deleted and an NSG flow log is linked to it, the flow log cannot be deleted.

Whether via the Azure portal or the Azure CLI

I've tried deleting only the flow log, only the region watcher, deleting the resource group. Nothing works.

### Related command

az network watcher flow-log delete --name xxxxxxx --location xxxxxx
### Errors

(SubnetNotFoundForFlowLog) Subnet resource /subscriptions/xxxxxxx/resourceGroups/xxxxxxx/providers/Microsoft.Network/VirtualNetworks/xxxxxxx/subnets/xxxxxxx passed for the flow log does not exist.
Code: SubnetNotFoundForFlowLog

Message: Subnet resource /subscriptions/xxxxxxxx/resourceGroups/xxxxxx/providers/Microsoft.Network/VirtualNetworks/VirtualNetworks/xxxxxxx/subnets/xxxxxxx passed for the flow log does not exist.

### Issue script & Debug output

/

### Expected behavior

Allow to delete NSG Flow if subnet has been deleted

### Environment Summary

azure-cli 2.73.0

core 2.73.0
telemetry 1.1.0

Extensions:
containerapp 1.1.0b4
rdbms-connect 1.0.7
serviceconnector-passwordless 3.3.1

Dependencies:
msal 1.32.3
azure-mgmt-resource 23.3.0

Python location '/opt/homebrew/Cellar/azure-cli/2.73.0/libexec/bin/python'
Config directory '/Users/***/.azure'
Extensions directory '/Users/***/.azure/cliextensions'

Python (Darwin) 3.12.10 (main, Apr 8 2025, 11:35:47) [Clang 16.0.0 (clang-1600.0.26.6)]

Legal docs and information: aka.ms/AzureCliLegal

### Additional context

_No response_