Add tests for ShowBgpVrf with IPv6 arguments

Author: Kani999

src/genie/libs/parser/iosxr/tests/ShowBgpVrf/cli/equal/golden_output_8_arguments.json

@@ -0,0 +1,4 @@
+{
+    "vrf": "xNet",
+    "address_family": "ipv6 unicast"
+}