install_arch: use versionless bootstrap tarball

nl6720requested to merge
nl6720/infrastructure:versionless-bootstrap into master

Since release 2022.07.01, there is a versionless bootstrap tarball file (archlinux-bootstrap-x86_64.tar.gz). See https://github.com/pierres/archiso-manager/pull/12.

latest is a valid version, so there is no need to check for the exact version number anymore.

Merge request reports