test(e2e): wait for marker_unique_id.html e2e test

Sometimes, Cypress takes the screenshot for marker_unique_id.html early,
before mermaid has finished rendering the diagrams.

Fixes: 924c9e913b

Co-authored-by: Sidharth Vinod <sidharthv96@gmail.com>

cypress/platform/marker_unique_id.html

@@ -42,7 +42,8 @@
     </pre>
     <script type="module">
       import mermaid from './mermaid.esm.mjs';
-      mermaid.initialize({ startOnLoad: true, logLevel: 0 });
+      mermaid.initialize({ startOnLoad: false, logLevel: 0 });
+      await mermaid.run();
 
       if (window.Cypress) {
         window.rendered = true;