Increase network-service-in-process flag expiration

Change-Id: I6716b187bcbdaf10bbe547ec0124a272977175cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1761136
Auto-Submit: Clark DuVall <cduvall@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688499}

chrome/browser/flag-metadata.json

@@ -2361,7 +2361,7 @@
   {
     "name": "network-service-in-process",
     "owners": [ "network-service-dev" ],
-    "expiry_milestone": 76
+    "expiry_milestone": 84
   },
   {
     "name": "new-net-error-page-ui",