Fix wrong variable for COOP + sandbox check

Closes #8511.

source

@@ -91492,7 +91492,7 @@ location.href = '#foo';</code></pre>
        <var>request</var>'s <span data-x="concept-request-referrer">referrer</span>.</p></li>
 
        <li>
-        <p>If <var>sandboxFlags</var> is not empty and <var>responseCOOP</var>'s <span
+        <p>If <var>finalSandboxFlags</var> is not empty and <var>responseCOOP</var>'s <span
         data-x="coop-struct-value">value</span> is not "<code
         data-x="coop-unsafe-none">unsafe-none</code>", then set <var>response</var> to an
         appropriate <span>network error</span> and <span>break</span>.</p>