[release-branch.go1.25] spec: update spec date to match release date
Ths spec date in the 1.25 release branch dates back to Feb 2025
which is rather confusing. Moving it forward to 1.25 release date.
Fixes #75743.
Change-Id: Ibb2da5dc238a3b876862eef802e90bee6326d6b5
Reviewed-on: https://go-review.googlesource.com/c/go/+/709515
Auto-Submit: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Alan Donovan <adonovan@google.com> Reviewed-by: Robert Griesemer <gri@google.com>