Backport app/models/environment.rb

# app/models/environment.rb

  def deployment_platform
    project.deployment_platform(environment: self)
  end

  def deployment_variables
    deployment_platform&.predefined_variables || []
  end

# app/models/ci/build.rb
def variables(environment: persisted_environment)
   ...
   variables += project.container_registry_variables
   variables += environment.deployment_variables if has_environment?
   variables += project.auto_devops_variables
   ...
end

--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -1556,10 +1556,6 @@ class Project < ActiveRecord::Base
       ProtectedTag.protected?(self, ref)
   end

-  def deployment_variables(environment: nil)
-    deployment_platform(environment: environment)&.predefined_variables || []
-  end
-
   def auto_devops_variables
     return [] unless auto_devops_enabled?

---

The following discussion from !3603 (merged) should be addressed:

• @dosuken123 started a discussion:

  This should be backport