a11y: do not use <label> for readonly single checkbox (#71089)

wcs/qommon/form.py

@@ -767,10 +767,11 @@ class CheckboxWidget(QuixoteCheckboxWidget):
             data_attrs = ' '.join('%s="%s"' % x for x in attrs.items() if x[0].startswith('data-'))
             # more elaborate markup so standalone checkboxes can be applied a
             # custom style.
+            label_tag = 'span' if 'readonly' in self.attrs else 'label'
             return (
-                htmltext('<label %s>%s<span>' % (data_attrs, checkbox))
+                htmltext('<%s %s>%s<span>' % (label_tag, data_attrs, checkbox))
                 + str(inline_title)
-                + htmltext('</span></label>')
+                + htmltext('</span></%s>' % label_tag)
             )
         return checkbox