Update articles/vpn-gateway/tutorial-protect-vpn-gateway.md

Corrected alt text

Author: PMEds28

articles/vpn-gateway/tutorial-protect-vpn-gateway.md

@@ -30,7 +30,7 @@ In this tutorial, you learn how to:
 
 The following diagram shows the virtual network and the VPN gateway created as part of this tutorial.
 
-:::image type="content" source="./media/tutorial-create-gateway-portal/gateway-diagram.png" alt-text="VNet and VPN gateway diagram.":::
+:::image type="content" source="./media/tutorial-create-gateway-portal/gateway-diagram.png" alt-text="Diagram showing VNet and VPN gateway.":::
 
 ## Prerequisites