fix Median operation returns incorrect result for unsorted odd-length inputs

[williballenthin]

closes #2239

AI disclosure
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[CLAassistant]

All committers have signed the CLA.

[GCHQDeveloper581]

@williballenthin - just to make you aware that the recent change to the PR template and the CONTRIBUTING file are, at this stage, to enable us to track the use of AI tools rather than an indication that we can (at the moment) accept contributions using them.

Whilst we are very hopeful that this will be allowed in (hopefully the near) future, at this stage we aren't able to merge these PRs.

[williballenthin]

Acknowledged, thanks for the context @GCHQDeveloper581. If you end up accepting the PRs, great! If not, I understand, too.

In another project I maintain, we're getting loads of AI-generated PRs every day. While the sudden interest is nice, I think we ultimately move slower because we have so much low-quality content to review.