test(repository): use `system.platform[:codename]` [skip ci]

Tested:

* https://gitlab.com/myii/nginx-formula/-/pipelines/470231421

test/integration/passenger/controls/repository.rb

   repo_file = '/etc/yum.repos.d/passenger.repo'
   repo_url = 'https://oss-binaries.phusionpassenger.com/yum/passenger/el/$releasever/$basearch'
 when 'debian'
-  # Inspec does not provide a `codename` matcher, so we add ours
-  finger_codename = {
-    'ubuntu-18.04' => 'bionic',
-    'ubuntu-20.04' => 'focal',
-    'debian-9' => 'stretch',
-    'debian-10' => 'buster',
-    'debian-11' => 'bullseye'
-  }
-  codename = finger_codename[system.platform[:finger]]
-
+  codename = system.platform[:codename]
   repo_keyring = '/usr/share/keyrings/phusionpassenger-archive-keyring.gpg'
   repo_file = "/etc/apt/sources.list.d/phusionpassenger-official-#{codename}.list"
-  # rubocop:disable Metrics/LineLength
+  # rubocop:disable Layout/LineLength
   repo_url = "deb [signed-by=#{repo_keyring}] https://oss-binaries.phusionpassenger.com/apt/passenger #{codename} main"
-  # rubocop:enable Metrics/LineLength
+  # rubocop:enable Layout/LineLength
 end
 
 control 'Phusion-passenger repository keyring' do