Upgrade eetcd to 0.3.5 (backport #4499) (backport #4500)

[mergify]

This is an automatic backport of pull request #4500 done by Mergify.
Cherry-pick of 10b8b59 has failed:

On branch mergify/bp/v3.9.x/pr-4500
Your branch is up to date with 'origin/v3.9.x'.

You are currently cherry-picking commit 10b8b59f38.
  (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:   deps/rabbitmq_peer_discovery_etcd/Makefile
	modified:   release-notes/3.9.15.md

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   release-notes/3.10.0.md

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

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[michaelklishin]

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