Html required validation still not working for radios element

Seems that #2945890: Html required validation not working for radios element doesn't fix the HTML5 validation problems for "radios" webform elements.

Steps to reproduce:

- install and enable webform module (version 8.x-5.0-rc18) e.g. by using simplytest.me
- add a new webform
- add a "radios" element e.g. call it "gender"
- add 2 options e.g. "male" and "female"
- turn on form validation (by marking the "Required" checkbox) and enter some text into "Required message"
- view your new webform and submit it without selecting a radio button option
- you will get a system form validation error message in your messages block at the top of the page AFTER a form submit, but the expected behaviour would be: to get a HTML5 validation error message on your radio buttons group (inside the form) BEFORE form submit (server-side processing)

Causal research:

The committed patch in #2945890: Html required validation not working for radios element adds 2 jQuery selectors and the first of them
.js-webform-type-radios[required="required"],
should "fire" in our case, but the wrapping element doesn't have a "required" attribute at all.
So by adding a new selector
.js-webform-type-radios.required,
between the 2 existing selectors in the /js/webform.element.radios.js file the expected behaviour can be achieved.

But the real question is: Why is the required="required" attribute missing for the radio buttons group wrapping fieldset?