Upgrade to Bootsnap 1.4.6

This upgrade makes it possible to pre-compute a Bootsnap cache for a containerized system, since the ruby_platform header is no longer dependent on uname -v--which changes depending on the host kernel--but rather on the glibc version: https://github.com/Shopify/bootsnap/pull/283

Full list of changes: https://github.com/Shopify/bootsnap/compare/v1.4.5..v1.4.6