rabbit_feature_flags: Fix formatting of the logged list of feature flags (backport #7232)

[mergify]

This is an automatic backport of pull request #7232 done by Mergify.
Cherry-pick of 10d3242 has failed:

On branch mergify/bp/v3.11.x/pr-7232
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You are currently cherry-picking commit 10d3242133.
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	both modified:   deps/rabbit/src/rabbit_ff_registry_factory.erl

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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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