Extend WebAuthn BLE support flag availability

Change the expiry for the flag to turn on BLE support for Web
Authentication to M-82, to prevent its removal from chrome://flags.

Change-Id: I8c50aeded7a28aea2af4dbbd3460757e59767ddb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1762268
Commit-Queue: Ken Buchanan <kenrb@chromium.org>
Commit-Queue: Nina Satragno <nsatragno@chromium.org>
Reviewed-by: Nina Satragno <nsatragno@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688523}

chrome/browser/flag-metadata.json

@@ -1809,7 +1809,7 @@
   {
     "name": "enable-web-authentication-ble-support",
     "owners": [ "webauthn-team@google.com" ],
-    "expiry_milestone": 76
+    "expiry_milestone": 82
   },
   {
     "name": "enable-web-authentication-cable-support",