[Flag] Update enable-experimental-kernel-vm-support flag

Extends the enable-experimental-kernel-vm-support flag lifetime until
M82.

Bug: none
Change-Id: Ia66b829cc3bf47bc8d9f2017c6bf0db589cd96c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1860530Reviewed-by: Nicholas Verne <nverne@chromium.org>
Commit-Queue: Nicholas Verne <nverne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708101}

chrome/browser/flag-metadata.json

@@ -1268,7 +1268,7 @@
   {
     "name": "enable-experimental-kernel-vm-support",
     "owners": [ "jflat", "zwisler" ],
-    "expiry_milestone": 78
+    "expiry_milestone": 82
   },
   {
     "name": "enable-experimental-productivity-features",