Add rubygems 3.2.8, remove rubygems 3.2.7
Add rubygems 3.2.8, remove rubygems 3.2.7

for stack(s) cflinuxfs3 [#176773146]

cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack,cloudfoundry/ruby-buildpack