Adjust sizing of checks and radios (#31383)

Moves from 1.25em to 1em to better support custom font-size-base values. Most common would probably be .875rem (14px) and current sizing garbles that into 1.09-ish, thus causing the rendering issues in #31269

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Co-authored-by: Martijn Cuppens <martijn.cuppens@gmail.com>

scss/_variables.scss

@@ -658,7 +658,7 @@ $input-height-lg:                       add($input-line-height * 1em, add($input
 $input-transition:                      border-color .15s ease-in-out, box-shadow .15s ease-in-out !default;
 
 
-$form-check-input-width:                  1.25em !default;
+$form-check-input-width:                  1em !default;
 $form-check-min-height:                   $font-size-base * $line-height-base !default;
 $form-check-padding-left:                 $form-check-input-width + .5em !default;
 $form-check-margin-bottom:                .125rem !default;