Add 6.6 release notes

_locales/en/messages.json

@@ -6458,5 +6458,9 @@
   "icu:WhatsNew__v6.5--1": {
     "messageformat": "It's now possible to search your message history for individual characters in Chinese and Japanese.",
     "description": "Release notes for v6.5"
+  },
+  "icu:WhatsNew__v6.6--0": {
+    "messageformat": "Help us test several reliability and performance improvements for voice and video calls. This beta release also includes a few bug fixes and some small UI updates (look for the new link preview enhancements!). Thank you for being a beta tester, and please reach out to us on the community forum if you spot any bugs.",
+    "description": "Release notes for v6.6"
   }
 }

ts/components/WhatsNewModal.tsx

@@ -31,11 +31,7 @@ const releaseNotes: ReleaseNotesType = {
   version: window.getVersion?.(),
   features: [
     {
-      key: 'icu:WhatsNew__v6.5--0',
-      components: undefined,
-    },
-    {
-      key: 'icu:WhatsNew__v6.5--1',
+      key: 'icu:WhatsNew__v6.6--0',
       components: undefined,
     },
   ],