Fix deprecation warning when rendering "xml.atom"

This fixes the following deprecation warning:

  DEPRECATION WARNING: Rendering actions with '.' in the name is
  deprecated: layouts/xml.atom (called from render at
  /builds/gitlab-org/gitlab/app/controllers/application_controller.rb:133)

app/controllers/concerns/issuable_collections_action.rb

@@ -17,7 +17,7 @@ module IssuableCollectionsAction
 
     respond_to do |format|
       format.html
-      format.atom { render layout: 'xml.atom' }
+      format.atom { render layout: 'xml' }
     end
   end
 

app/controllers/dashboard/projects_controller.rb

@@ -23,7 +23,7 @@ class Dashboard::ProjectsController < Dashboard::ApplicationController
       end
       format.atom do
         load_events
-        render layout: 'xml.atom'
+        render layout: 'xml'
       end
       format.json do
         render json: {

app/controllers/groups_controller.rb

@@ -235,7 +235,7 @@ class GroupsController < Groups::ApplicationController
 
   def render_details_view_atom
     load_events
-    render layout: 'xml.atom', template: 'groups/show'
+    render layout: 'xml', template: 'groups/show'
   end
 
   # rubocop: disable CodeReuse/ActiveRecord

app/controllers/projects/commits_controller.rb

@@ -30,7 +30,7 @@ class Projects::CommitsController < Projects::ApplicationController
 
     respond_to do |format|
       format.html
-      format.atom { render layout: 'xml.atom' }
+      format.atom { render layout: 'xml' }
 
       format.json do
         pager_json(

app/controllers/projects/issues_controller.rb

@@ -81,7 +81,7 @@ class Projects::IssuesController < Projects::ApplicationController
 
     respond_to do |format|
       format.html
-      format.atom { render layout: 'xml.atom' }
+      format.atom { render layout: 'xml' }
       format.json do
         render json: {
           html: view_to_html_string("projects/issues/_issues"),

app/controllers/projects/merge_requests_controller.rb

@@ -93,7 +93,7 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
 
     respond_to do |format|
       format.html
-      format.atom { render layout: 'xml.atom' }
+      format.atom { render layout: 'xml' }
       format.json do
         render json: {
           html: view_to_html_string("projects/merge_requests/_merge_requests")

app/controllers/projects/tags_controller.rb

@@ -42,7 +42,7 @@ class Projects::TagsController < Projects::ApplicationController
       status = @tags_loading_error ? :service_unavailable : :ok
 
       format.html { render status: status }
-      format.atom { render layout: 'xml.atom', status: status }
+      format.atom { render layout: 'xml', status: status }
     end
   end
   # rubocop: enable CodeReuse/ActiveRecord

app/controllers/projects_controller.rb

@@ -173,7 +173,7 @@ class ProjectsController < Projects::ApplicationController
       format.atom do
         load_events
         @events = @events.select { |event| event.visible_to_user?(current_user) }
-        render layout: 'xml.atom'
+        render layout: 'xml'
       end
     end
   end

app/controllers/users_controller.rb

@@ -35,7 +35,7 @@ class UsersController < ApplicationController
 
       format.atom do
         load_events
-        render layout: 'xml.atom'
+        render layout: 'xml'
       end
 
       format.json do

spec/controllers/projects_controller_spec.rb

@@ -1590,14 +1590,18 @@ RSpec.describe ProjectsController do
 
       get :show, format: :atom, params: { id: public_project, namespace_id: public_project.namespace }
 
-      expect(response).to render_template('xml.atom')
+      expect(response).to have_gitlab_http_status(:success)
+      expect(response).to render_template(:show)
+      expect(response).to render_template(layout: :xml)
       expect(assigns(:events)).to eq([event])
     end
 
     it 'filters by calling event.visible_to_user?' do
       get :show, format: :atom, params: { id: public_project, namespace_id: public_project.namespace }
 
-      expect(response).to render_template('xml.atom')
+      expect(response).to have_gitlab_http_status(:success)
+      expect(response).to render_template(:show)
+      expect(response).to render_template(layout: :xml)
       expect(assigns(:events)).to eq([event])
     end
   end