Fix pytest warning

[pquentin]

Applying pytest.mark.usefixtures on a pytest fixture does not have any effect, see https://docs.pytest.org/en/stable/deprecations.html#applying-a-mark-to-a-fixture-function. The idea was to call wipe_cluster, but we do it explicitly now anyways.

Relates elastic/elasticsearch-serverless-python#41

[github-actions]

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