Only query radios that are within the same form

By doing this alongside checking the name we only run setAttributes on
the radio inputs that could change.

src/govuk/components/radios/radios.js

@@ -46,16 +46,16 @@ Radios.prototype.setAttributes = function ($input) {
 }
 
 Radios.prototype.handleClick = function (event) {
+  var $clickedInput = event.target
   // We only want to handle clicks for radio inputs
-  if (event.target.type !== 'radio') {
+  if ($clickedInput.type !== 'radio') {
     return
   }
   // Because checking one radio can uncheck a radio in another $module,
-  // we need to call set attributes on all radios in the document
+  // we need to call set attributes on all radios in the form owner
   //
   // We also only want radios which have aria-controls, as they support conditional reveals.
-  var $allInputs = document.querySelectorAll('input[type="radio"][aria-controls]')
-  var $clickedInput = event.target
+  var $allInputs = $clickedInput.form.querySelectorAll('input[type="radio"][aria-controls]')
   nodeListForEach($allInputs, function ($input) {
     // In radios, only radios with the same name will affect each other.
     if ($clickedInput.name === $input.name) {