Update flag expiration for "enable-avoid-flash-between-navigation"

R=pdr@chromium.org

Bug: None
Change-Id: Ia263c5503c93fffcb913fa5bfc58bf23edac2e85
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1760882
Auto-Submit: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688553}

chrome/browser/flag-metadata.json

@@ -954,7 +954,7 @@
   {
     "name": "enable-avoid-flash-between-navigation",
     "owners": [ "schenney", "paint-dev" ],
-    "expiry_milestone": 76
+    "expiry_milestone": 80
   },
   {
     "name": "enable-backdrop-filter",