Update copyright in 2024 and 2025 editions of html spec

[gesa]

Now that the corrigenda have been voted on and approved at the 111th meeting of TC39, the 2024 and 2025 editions of ECMA-262 must be updated with the approved copyright. The Ecma "alternative" copyright statement can be found at https://ecma-international.org/policies/by-ipr/ecma-text-copyright-policy/#alternative-copyright-notice.

[ljharb]

2024? Usually we don't update "N - 1" years once "N" year is out. (we certainly can update both, i'm just confirming)