Do not confirm MQTT messages if in partition (backport #9523)

[mergify]

This is an automatic backport of pull request #9523 done by Mergify.
Cherry-pick of d8ecc66 has failed:

On branch mergify/bp/v3.12.x/pr-9523
Your branch is up to date with 'origin/v3.12.x'.

You are currently cherry-picking commit d8ecc66a8e.
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  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
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	both modified:   deps/rabbitmq_mqtt/src/rabbit_mqtt_processor.erl

no changes added to commit (use "git add" and/or "git commit -a")

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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