message: update the beta backport example to a more recent PR
diff: @@ -20,10 +20,10 @@ a backport is those tagged
  [both `beta-nominated` and `beta-accepted`](https://github.com/rust-lang/rust/pulls?q=is%3Apr+label%3Abeta-accepted+is%3Aclosed+label%3Abeta-nominated).
  So now somebody needs to go through those PR's and cherry-pick their commits to
  -the beta branch. Those cherry-picks are then submitted as a PR _against the beta
  -branch_, with a title started with `[beta]` (so reviewers can see its
  +the beta branch. Those cherry-picks are then submitted as a PR _against the
  +beta branch_, with a title started with `[beta]` (so reviewers can see its
  specialness). The OP of that PR should contain links to all the PRs being
  -backported. [Here's an example](https://github.com/rust-lang/rust/pull/36634).
  +backported. [Here's an example](https://github.com/rust-lang/rust/pull/64097).
  Anybody can make these PRs!
  After that a reviewer needs to verify that the backport looks correct, that it's
  