Backport "Set default source version to 3.5" to 3.5.0#20583

WojciechMazur merged 1 commit intoscala:release-3.5.0scala/scala3:release-3.5.0from

WojciechMazur:backport-3.5.0/20441WojciechMazur/dotty:backport-3.5.0/20441Copy head branch name to clipboard