What's New: Extend flag to M110

Holdback study is still needed for the next few What's New milestones
(M108, M110).

Bug: 1219381
Change-Id: I04c6589125661dbfc02ffdda620561755079b869
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3842914
Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1037847}

chrome/browser/flag-metadata.json

@@ -925,7 +925,7 @@
   {
     "name": "chrome-whats-new-ui",
     "owners": [ "rbpotter" ],
-    "expiry_milestone": 106
+    "expiry_milestone": 110
   },
   {
     "name": "chrome-wide-echo-cancellation",