Ignore dots in slugs when rendering custom pages

We were getting a warning in one of the tests:

DEPRECATION WARNING: Rendering actions with '.' in the name is
deprecated: application/nonExistentJavaScript.js

I haven't found a case where the behavior on production environments is
different due to this change; the application seems to behave the same
way as it used to. So I'm not adding tests for this change.

app/controllers/pages_controller.rb

@@ -11,7 +11,7 @@ class PagesController < ApplicationController
       @cards = @custom_page.cards
       render action: :custom_page
     else
-      render action: params[:id]
+      render action: params[:id].split(".").first
     end
   rescue ActionView::MissingTemplate
     head :not_found, content_type: "text/html"