[Tech Debt] Update detect-new-version-and-upload-artifacts task packaging logic for PHP

[brayanhenao]

Context

This task interacts with both Gemfiles (buildpacks-ci and the buildpack that is being packaged) in the case in which the Buildpack is packaged with buildpack-packager. This only happens with PHP right now since is the only buildpack that uses the old package logic.

On https://github.com/cloudfoundry/php-buildpack/pull/815 we updated the PHP Buildpack Gemfile required Ruby version to 3.0. Now that the detect-and-upload task runs for the PHP Buildpack, it fails because of the ruby version used in the cfbuildpacks/ci image on which the task is being run.

Temporary solution

In #245 we updated the task to download the old PHP Gemfile (Ruby 2) just to install and package the buildpack. This should be changed once bionic/cflinuxfs3 is deprecated and the ci image/buildpacks-ci dockerfile is updated.