[3.5] backport #17176 fix learner metric incorrect issue

[YaoC]

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

Backport #17176 to release-3.5

Fix #17175

[k8s-ci-robot]

Hi @YaoC. Thanks for your PR.

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[YaoC]

I'm trying to backport #17176 but I found that the e2e test code for release-3.5 and release-3.4 is quite different from the one in the main branch. Should I first backport the corresponding e2e framework or rewrite a new e2e case? Any suggestions? @ahrtr @serathius

[ahrtr]

In general, we need to evaluate it case by case. My thought on this are:

• We can try to backport the test framework and common utilities. But if it (backporting) needs huge effort, It's also accepted to directly implement some utilities (e.g. WaitLeader) in 3.5 and 3.4 if it just needs minor effort
• It's open to discussion. cc @jmhbnz @serathius @fuweid @amit-rastogi