Extend HaTS Flag Expiration to M80

This is still currently used for testing.

BUG=979530
TBR=weili@chromium.org

Change-Id: Ie837afa0f996faf22303459ffbfdb03c3182b938
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1857204Reviewed-by: Robert Liao <robliao@chromium.org>
Commit-Queue: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705300}

chrome/browser/flag-metadata.json

@@ -2264,7 +2264,7 @@
   {
     "name": "happiness-tracking-surveys-for-desktop",
     "owners": [ "//chrome/browser/ui/hats/OWNERS" ],
-    "expiry_milestone": 78
+    "expiry_milestone": 80
   },
   {
     "name": "happiness-tracking-surveys-for-desktop-demo",
@@ -2272,7 +2272,7 @@
     // 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": 78
+    "expiry_milestone": 80
   },
   {
     "name": "hardware-media-key-handling",