Draft: Introduce Gitlab.next_rails? to run Rails 7.1 tests

What does this MR do and why?

Similar to Draft: Introduce Gitlab.next_rails? to run Rail... (!160895 - closed), but this MR specifies BUNDLE_GEMFILE: "Gemfile.next" to install gems for Rails 7.1 version.

app/models/preloaders/project_policy_preloader.rb

@@ -8,7 +8,7 @@ def initialize(projects, current_user)
     end
 
     def execute
-      return if projects.is_a?(ActiveRecord::Relation) && projects.null_relation?
+      return if projects.none?
 
       ActiveRecord::Associations::Preloader.new(
         records: projects,