[release]: Update Flatpak manifest

Author: mr-cheffy

app.zen_browser.zen.metainfo.xml

@@ -59,7 +59,7 @@
     <control>keyboard</control>
   </supports>
   <releases>
-    <release version="1.15.3b" date="2025-09-01T23:22:00.226Z">
+    <release version="1.15.3b" date="2025-09-02T18:55:22.689Z">
       <url type="details">https://zen-browser.app/release-notes/1.15.3b</url>
     </release>
     <release version="1.15.2b" date="2025-08-29T08:07:22.260Z">