Update New-AzVirtualNetworkSubnetConfig.md (#22561)

`New-AzVirtualSubnetConfig` does not exists but `New-AzVirtualNetworkSubnetConfig` does.

src/Network/Network/help/New-AzVirtualNetworkSubnetConfig.md

@@ -69,8 +69,8 @@ New-AzVirtualNetwork -Name MyVirtualNetwork -ResourceGroupName TestResourceGroup
 ```
 
 This example creates two new subnet configurations using the 
-    New-AzVirtualSubnetConfig cmdlet, and then uses them to create a virtual network. 
-    The New-AzVirtualSubnetConfig template only creates an in-memory representation of 
+    New-AzVirtualNetworkSubnetConfig cmdlet, and then uses them to create a virtual network. 
+    The New-AzVirtualNetworkSubnetConfig template only creates an in-memory representation of 
     the subnet. In this example, the frontendSubnet has CIDR 10.0.1.0/24 and references a 
     network security group that allows RDP access. The backendSubnet has CIDR 10.0.2.0/24 and 
     references the same network security group.