[BUG] ExpressRouteCircuitConnections_CreateOrUpdate - updating `authorizationKey` doesn't apply if it's the only change in the request

### API Spec link

https://github.com/Azure/azure-rest-api-specs/blob/main/specification/network/resource-manager/Microsoft.Network/Network/stable/2025-01-01/expressRouteCircuit.json#L661

### API Spec version

2025-01-01

### Describe the bug

The API ignores updates to `authorizationKey` unless accompanied by another change, e.g. `expressRouteGatewayBypass`

### Expected behavior

The `authorizationKey` field is updatable without having to arbitrarily modify a different field for the service to recognize there is a change and move to the `Updating` provisioningState

### Actual behavior

API ignores updates to just `authorizationKey`

### Reproduction Steps

- Provision an express route connection with `authorizationKey` set
- Update `authorizationKey` and send another PUT request (e.g. `authorizationKey` from a valid value -> null / empty string)
- Observe resource never changes `provisioningState` and the `authorizationKey` parameter in the next GET is unchanged / still present.

### Environment

terraform

Start at the ExpressRouteCircuitConnections_CreateOrUpdate definition in specification/network/resource-manager/Microsoft.Network/Network/stable/2025-01-01/expressRouteCircuit.json around line 661. Compare the declared behavior of authorizationKey with the reproduction steps and determine how an authorizationKey-only update is represented. Done means the 2025-01-01 specification accurately describes and supports that update without an unrelated field change.

Written by the indexing model from the issue text.