[HaTS] Extend HaTS expiration date to M84

Extends HaTS flags for two more milestones to allow more testing.

Change-Id: I484e5f7d228fd1e07386aed41643c62c0d039aa1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2095334
Reviewed-by: Robert Liao <robliao@chromium.org>
Commit-Queue: Wei Li <weili@chromium.org>
Cr-Commit-Position: refs/heads/master@{#748529}

chrome/browser/flag-metadata.json

@@ -2389,15 +2389,15 @@
   {
     "name": "happiness-tracking-surveys-for-desktop",
     "owners": [ "//chrome/browser/ui/hats/OWNERS" ],
-    "expiry_milestone": 82
+    "expiry_milestone": 84
   },
   {
     "name": "happiness-tracking-surveys-for-desktop-demo",
     "owners": [ "//chrome/browser/ui/hats/OWNERS" ],
     // A debugging and demo flag to allow UI/dev/testing team to always show the UI
     // components for the survey without being limited by the triggering mechanism.
     // This flag should expire along with the above feature flag.
-    "expiry_milestone": 82
+    "expiry_milestone": 84
   },
   {
     "name": "happiness-tracking-surveys-for-desktop-settings",