anyway we don't need authorization here.
Also retry does not seem to work in the original version, so let's
extend this with retries as a separate github action later.

because it randomly fails on authorization like:
https://github.com/ruby/ruby/runs/190887455
Also the backoff seems too short. Maybe we need tool/travis_retry.sh for
this too.

Cloning ruby/ruby does not need authorization. We don't need to use
actions/checkout.

Not using official travis_retry.bash, because it's not supporting to
modify backoff seconds.
https://github.com/travis-ci/travis-build/blob/0ad8f1886b2c31994d847e126dc5842b7b3513e3/lib/travis/build/bash/travis_retry.bash

Not using official `travis_apt_get_update` function because it does not
propagate exit status to be used by retries.
https://github.com/travis-ci/travis-build/blob/0ad8f1886b2c31994d847e126dc5842b7b3513e3/lib/travis/build/bash/travis_apt_get_update.bash

Co-Authored-By: Nobuyoshi Nakada <nobu@ruby-lang.org>