Update Quiet Notifications Flag expiry_milestone to M83.

Updating this flag to M83, as we might still decide to experiment with different UI details, after launching.


Bug: 986737
Change-Id: I049d06e4f909f2375c4f12065b61d68f1106b212
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1917766Reviewed-by: Mike West <mkwst@chromium.org>
Commit-Queue: Kamila Hasanbega <hkamila@google.com>
Cr-Commit-Position: refs/heads/master@{#715642}

chrome/browser/flag-metadata.json

@@ -3087,7 +3087,7 @@
   {
     "name": "quiet-notification-prompts",
     "owners": [ "engedy", "mkwst", "andypaicu", "hkamila" ],
-    "expiry_milestone": 80
+    "expiry_milestone": 83
   },
   {
     "name": "reader-mode-heuristics",