The library pack's bytes depend on the builder's time zone #51

The first weekly refresh since the pack was split (#48) rewrote all 106 archives — the 105 parts and libraries.h5p — with no library changed: its change list is empty.

Cause. build-libraries.mjs and packages/libraries/scripts/parts.mjs write every entry with lastModDate: new Date(Date.UTC(2000, 0, 1)). A zip records a wall-clock time with no zone, and zip.js takes it from the Date's local fields (getHours()). The committed pack was built at UTC+2, so its entries say 02:00; CI builds in UTC and writes 00:00. Every entry's name, CRC, sizes, method and extra field are the same in both, checked archive by archive.

Also. The workflow's change list keeps only lines starting with H5P, so a new version of FontAwesome, jQuery.ui, flowplayer, Shepherd or TimelineJS would show an empty list too. And when no library changed it still opens a pull request saying the hub changed.

Fix. A wall-clock date that writes what pack 1.0.0 shipped (2000-01-01 02:00) in any time zone, so no release is needed for this; a test that builds in two time zones; the change list matching every library; and the workflow stopping, rather than opening a pull request, when files changed and no library did. #48 is then closed unmerged.