net/netip: use IPv6Loopback in TestIPProperties

Change-Id: I667bdaf52e9d32cd89e396616057bc57ecaffe09
Reviewed-on: https://go-review.googlesource.com/c/go/+/463836
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
diff --git a/src/net/netip/netip_test.go b/src/net/netip/netip_test.go
index b8719f6..0f80bb0 100644
--- a/src/net/netip/netip_test.go
+++ b/src/net/netip/netip_test.go
@@ -585,7 +585,6 @@
 		lluZone6 = mustIP("fe80::1%eth0")
 
 		loopback4 = mustIP("127.0.0.1")
-		loopback6 = mustIP("::1")
 
 		ilm6     = mustIP("ff01::1")
 		ilmZone6 = mustIP("ff01::1%eth0")
@@ -677,7 +676,7 @@
 		},
 		{
 			name:     "loopback v6Addr",
-			ip:       loopback6,
+			ip:       IPv6Loopback(),
 			loopback: true,
 		},
 		{