go/packages: use go.dev/issue links in comment

Change-Id: I248213b1c112017b827c75fb23df39ce249ee180
Reviewed-on: https://go-review.googlesource.com/c/tools/+/642755
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Commit-Queue: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>

Author: ianlancetaylor

go/packages/packages.go

@@ -59,10 +59,10 @@ import (
 //
 // Unfortunately there are a number of open bugs related to
 // interactions among the LoadMode bits:
-//   - https://github.com/golang/go/issues/56633
-//   - https://github.com/golang/go/issues/56677
-//   - https://github.com/golang/go/issues/58726
-//   - https://github.com/golang/go/issues/63517
+//   - https://go.dev/issue/56633
+//   - https://go.dev/issue/56677
+//   - https://go.dev/issue/58726
+//   - https://go.dev/issue/63517
 type LoadMode int
 
 const (