[Patta]

A regression introduced in 13.1.2 prevents form submission when a required powermail checkbox group is present and the first checkbox is not selected.

The race-condition fix in c21df00 added a native validation check via reportValidity().

While powermail validates checkbox groups as a single logical field, native browser validation evaluates the required checkbox differently, which can cause valid submissions to be rejected.

Skip the native validation check when a required powermail checkbox group is present and continue to rely on powermail's existing validation for this case.

This keeps the race-condition fix in place while restoring the behaviour that worked prior to 13.1.2.

resolves #123