Update packages/scoped-custom-element-registry/test/Element.test.html.js

Co-authored-by: Russell Bicknell <bicknellr@gmail.com>

Author: jmcgavin

packages/scoped-custom-element-registry/test/Element.test.html.js

@@ -146,7 +146,7 @@ describe('Element', () => {
 
       expect($el.hasAttribute('foo')).to.be.false;
 
-      $el.setAttribute('foo');
+      $el.setAttribute('foo', '');
       $el.toggleAttribute('foo', true);
 
       expect($el.hasAttribute('foo')).to.be.true;