YH4F update Sponsor Logos

- [ ] increase space around Proxmox Logo
- [ ] ensure size of logo is appropriate
- [ ] add links to Sponsors webpage

fsfe.org/activities/yh4f/index.en.xhtml

@@ -185,8 +185,8 @@ You can find out more about the six inspiring projects <a href="/news/2024/news-
   </div>
 
   <div class="center">
-      <img src="https://pics.fsfe.org/uploads/medium/1d/bf/3b24fa0492ec0c1410ab0246a3a5.png"/>
-      <img src="https://pics.fsfe.org/uploads/original/15/ce/d78f723ae4105ed27d875c36150f.png" />
+     <a href="https://www.proxmox.com"> <img src="https://pics.fsfe.org/uploads/original/24/53/32ae8d70d491553a73dd8d917adb.png"/> </a>
+     <a href="https://openssf.org/"> <img src="https://pics.fsfe.org/uploads/original/15/ce/d78f723ae4105ed27d875c36150f.png" /> </a>
   </div>
 
    <div class="color-box background" data-color="android-blue">