Sort secret variables by key (fix #20870)

app/models/ci/variable.rb

 module Ci
   class Variable < ActiveRecord::Base
     extend Ci::Model
-    
+
     belongs_to :project, class_name: '::Project', foreign_key: :gl_project_id
 
     validates_uniqueness_of :key, scope: :gl_project_id
@@ -11,7 +11,9 @@ module Ci
       format: { with: /\A[a-zA-Z0-9_]+\z/,
                 message: "can contain only letters, digits and '_'." }
 
-    attr_encrypted :value, 
+    scope :order_key_asc, -> { reorder(key: :asc) }
+
+    attr_encrypted :value,
        mode: :per_attribute_iv_and_salt,
        insecure_mode: true,
        key: Gitlab::Application.secrets.db_key_base,

app/views/projects/variables/_table.html.haml

@@ -9,7 +9,7 @@
       %th Value
       %th
     %tbody
-      - @project.variables.each do |variable|
+      - @project.variables.order_key_asc.each do |variable|
         - if variable.id?
           %tr
             %td= variable.key