internal/stdlib: update stdlib index for Go 1.25.0

For golang/go#38706.

Change-Id: Iba4ed76ee548d2774ab9f43970a2ab629d316ef4
Reviewed-on: https://go-review.googlesource.com/c/tools/+/695417
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: gopherbot