Update copyright year to 2023 in `license.txt` and bundled themes.

Follow-up to [18201], [23306], [28064], [36855], [36856], [39659], [40241], [42424], [46719], [46720], [47025], [47026], [49915], [52427].
Built from https://develop.svn.wordpress.org/trunk@55024


git-svn-id: http://core.svn.wordpress.org/trunk@54557 1a063a9b-81f0-0310-95a4-ce76da25c4cd