Migrate from ubuntu-20.04 GitHub Actions

[marcoieni]

Move GitHub actions runner of https://github.com/rust-lang/rust from ubuntu 20.04 to ubuntu 22.04

zulip discussion: https://rust-lang.zulipchat.com/#narrow/channel/242791-t-infra/topic/GitHub.20will.20retire.20Ubuntu.2020.20runner.20on.201.20April/near/486541919