move check for api doc enabledness to before action

Otherwise there is double render happending and it is cleaner to use a
before action than to return when rendirng 404

app/controllers/api_docs_controller.rb

@@ -29,14 +29,19 @@
 #++
 
 class APIDocsController < ApplicationController
-  before_action :require_login
+  before_action :require_login,
+                :check_if_api_docs_enabled
   no_authorization_required! :index
 
   helper API::APIDocsHelper
 
   def index
-    render_404 unless Setting.apiv3_docs_enabled?
-
     render locals: { turbo_opt_out: true }
   end
+
+  private
+
+  def check_if_api_docs_enabled
+    render_404 unless Setting.apiv3_docs_enabled?
+  end
 end