v2.1: Update to the latest tokio (backport of #4411)

[mergify]

We were pinning to an ancient version of tokio because of allegged issues with RPC and the io loop. We've merged #3242 which should improve the io loop situation with RPCs.

Update to tokio so we finally pick up tokio-rs/tokio#6512 which fixes bad perf for timeouts.

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This is an automatic backport of pull request #4411 done by Mergify.

[mergify]

Cherry-pick of de754be has failed:

On branch mergify/bp/v2.1/pr-4411
Your branch is up to date with 'origin/v2.1'.

You are currently cherry-picking commit de754be2e.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   Cargo.toml

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   Cargo.lock
	both modified:   programs/sbf/Cargo.lock
	deleted by us:   svm/examples/Cargo.lock

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[t-nelson]

fixed it

[alexpyattaev]

as already approved by Trent.