release-24.2: raft: deflake non-determinisctic raft node tests

[blathers-crl]

Backport 1/1 commits from #133270 on behalf of @iskettaneh.

/cc @cockroachdb/release

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We sporadically see that some raft node_test tests fail due to the leader not being stable. This commit should reduce the chances of that happening by increasing the election timeout to 250ms (instead of 50ms).

I couldn't reproduce the bug locally with this change.

If the bug still happens, we can try to force leadership to make it more deterministic.

Fixes: #132992, #131676, #132205, #133048

Release note: None

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Release justification: backporting a deflake

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

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[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

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[cockroach-teamcity]

This change is