Update copyright

[muzimuzhi]

Currently this PR give "Yes" and "Yes""No" (see https://github.com/latex3/l3build/issues/325#issuecomment-1856592871) to the questions I asked in #325.

Questions:

• Is it ok to add 2023 to copyright notices to all l3build*.lua files even if some of them are not updated in 2023?
• Does l3build want to keep precise copyright year lists, like https://github.com/latex3/l3build/blob/1cae1aa62f94be10c99ffbddfa9851300ec0581d/l3build-help.lua#L3

Closes #325

[muzimuzhi]

With the single range copyright, lua code used to update copyright can be simplified too.