Network.PeerExpressRouteCircuitConnections_Get API cannot get the existing peer express route circuit connection

After tested, we found [Network.PeerExpressRouteCircuitConnections_Get](https://github.com/Azure/azure-rest-api-specs/blob/61b4ce18d89d493e94d15bb101786a6e8a675ac8/specification/network/resource-manager/Microsoft.Network/stable/2021-02-01/expressRouteCircuit.json#L808) API cannot get the existing peer express route circuit connection and throw below error message. If it's an issue, Please have a look. Thanks.

Error message:
```
Code: NotFound
Message: Resource /subscriptions/xx-xx-xx-xx/resourceGroups/xxxx/providers/Microsoft.Network/expressRouteCircuits/xxxx/peerings/AzurePrivatePeering/peerConnections/xxxx not found.
Details: []
```

Repro steps:
1. Create Resource Group
2. Create ExpressRoute Circuit A
3. Create ExpressRoute Circuit B
4. Create ExpressRoute Circuit Peering A for ExpressRoute Circuit A
5. Create ExpressRoute Circuit Peering B for ExpressRoute Circuit B
6. Create ExpressRoute Circuit Connection for ExpressRoute Circuit A
7. Invoke Network.PeerExpressRouteCircuitConnections_Get API but it says it cannot find this peer expressroute circuit connection

Start with specification/network/resource-manager/Microsoft.Network/stable/2021-02-01/expressRouteCircuit.json at the PeerExpressRouteCircuitConnections_Get definition. Reproduce the seven-step ExpressRoute setup and invoke the API, then compare the documented resource path with the path of the existing peer connection. Done means the cause is identified and the specification or API behavior is corrected and verified.

Written by the indexing model from the issue text.