Fix redis unit check to test if CI

[kdumontnu]

Currently, unit tests fail for me locally (eg. make test-backend).

[wxiaoguang]

• Skip redis test if redis-server not available #24641 (review)

I would suggest not doing so.
Keep the old logic will remind developers that "please remember to test the redis queue"
Since in most cases, developers only run single test, this test doesn't affect them.
And there is always a chance for developers to bypass it: CI=local make test-xxxx

I think it's better to clarify the failure message: please use "CI=local make test" if you want to run the full test but do not have a redis-server

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But if most people prefer to skip the redis queue test, I have no objection.

[kdumontnu]

zeripath beat me to it