Copyright year is updated on build

Description of problem:

Copyright year is updated on build (in configure)

Version of gnutls used:

3.6.13

Distributor of gnutls (e.g., Ubuntu, Fedora, RHEL)

openSUSE

How reproducible:

Always

Steps to Reproduce:

• build gnutls from scratch in current year and a later year (can use qemu -rtc base=)
• compare binaries

Actual results:

building today's version in 2025 produces Copyright (C) 2000-2025 Free Software Foundation, and others and differs from a binary built today.

Expected results:

Software builds should be reproducible. See https://reproducible-builds.org/ for why this matters.

!928 (comment 145264928) seems to be the preferred approach.

!1058 (closed) was considered to add too much work at max 1 commit/year