Fix when a script element is implicitly potentially render-blocking

Fixes whatwg#7893, which is a bug introduced by whatwg#7857.

source

@@ -60129,7 +60129,9 @@ o............A....e
 
   <p>A <code>script</code> element is <span>implicitly potentially render-blocking</span> if the
   element's <span data-x="concept-script-type">script's type</span> is set and is equal to
-  "<code data-x="">classic</code>", and the element is <span>"parser-inserted"</span>.</p>
+  "<code data-x="">classic</code>", the element is <span>"parser-inserted"</span>, and the
+  element does not have an <code data-x="attr-script-async">async</code> or
+  <code data-x="attr-script-defer">defer</code> attribute.</p>
 
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