Add deprecation message for openSUSE 15.4

We will stop building packages for openSUSE 15.4
by GitLab 16.8

Changelog: deprecated

Author: twk3

files/gitlab-cookbooks/package/libraries/omnibus_helper.rb

@@ -176,7 +176,8 @@ def self.deprecated_os_list
       'opensuseleap-15.2' => 'GitLab 14.5',
       'suse-12.2' => 'GitLab 14.5',
       'debian-9' => 'GitLab 15.2',
-      'opensuseleap-15.3' => 'GitLab 15.11'
+      'opensuseleap-15.3' => 'GitLab 15.11',
+      'opensuseleap-15.4' => 'GitLab 16.8'
     }
   end