Updates code using class_methods over module ClassMethods

lib/api/api_guard.rb

@@ -84,7 +84,7 @@ module API
       end
     end
-    module ClassMethods
+    class_methods do
       private
       def install_error_responders(base)

lib/api/projects_relation_builder.rb

@@ -2,7 +2,7 @@ module API
   module ProjectsRelationBuilder
     extend ActiveSupport::Concern
-    module ClassMethods
+    class_methods do
       def prepare_relation(projects_relation, options = {})
         projects_relation = preload_relation(projects_relation, options)
         execute_batch_counting(projects_relation)

lib/gitlab/github_import/representation/expose_attribute.rb

@@ -6,7 +6,7 @@ module Gitlab
       module ExposeAttribute
         extend ActiveSupport::Concern
-        module ClassMethods
+        class_methods do
           # Defines getter methods for the given attribute names.
           #
           # Example:

lib/gitlab/graphql/mount_mutation.rb

@@ -5,7 +5,7 @@ module Gitlab
     module MountMutation
       extend ActiveSupport::Concern
-      module ClassMethods
+      class_methods do
         def mount_mutation(mutation_class)
           # Using an underscored field name symbol will make `graphql-ruby`
           # standardize the field name

lib/static_model.rb

@@ -2,7 +2,7 @@
 module StaticModel
   extend ActiveSupport::Concern
-  module ClassMethods
+  class_methods do
     # Used by ActiveRecord's polymorphic association to set object_id
     def primary_key
       'id'