cmd/release: add linux-arm64

Updates golang/go#19082

Change-Id: I02cd4f0e06e1f405761967dd550cf6c7a638835a
Reviewed-on: https://go-review.googlesource.com/45913
Reviewed-by: Chris Broadfoot <cbro@golang.org>
diff --git a/cmd/release/release.go b/cmd/release/release.go
index 4b665aa..bff3b2c 100644
--- a/cmd/release/release.go
+++ b/cmd/release/release.go
@@ -180,6 +180,11 @@
 		Builder: "linux-amd64",
 	},
 	{
+		OS:      "linux",
+		Arch:    "arm64",
+		Builder: "linux-arm64-packet",
+	},
+	{
 		OS:      "freebsd",
 		Arch:    "386",
 		Builder: "freebsd-386-gce101",