Flaky test case: TestCompressedResponse

[yeya24]

https://github.com/cortexproject/cortex/actions/runs/11045392221/job/30684835319?pr=6237

It might be relevant to #5527

[afhassan]

The test failed because the order of headers in the expected and the actual PrometheusResponseHeader is different but the content is the same.