chore: tweak sponsor assets

Author: boojack

README.md

@@ -22,10 +22,10 @@ An open-source, self-hosted note-taking service. Your thoughts, your data, your
 
 ---
 
-[**LambdaTest** - Cross-browser testing cloud](https://www.lambdatest.com/?utm_source=memos&utm_medium=sponsor)
+[**TestMu AI** - The world’s first full-stack Agentic AI Quality Engineering platform](https://www.testmu.ai/?utm_source=memos&utm_medium=sponsor)
 
-<a href="https://www.lambdatest.com/?utm_source=memos&utm_medium=sponsor" target="_blank" rel="noopener">
-  <img src="https://www.lambdatest.com/blue-logo.png" alt="LambdaTest - Cross-browser testing cloud" height="50" />
+<a href="https://www.testmu.ai/?utm_source=memos&utm_medium=sponsor" target="_blank" rel="noopener">
+  <img src="https://usememos.com/sponsors/testmu.svg" alt="TestMu AI" height="36" />
 </a>
 
 ## Overview