fix depth inequality

[ocefpaf]

See TEOS-10/GSW-C#60 (comment)

[efiring]

Given that this repo is not used for development, perhaps it is better to let it be a record of the distributed Matlab version (from the official zip file), frozen at whatever points we try to match with C. As we use it, I think that making this Matlab repo diverge from the official versions might make work on the other languages more confusing. That does not restrict us from fixing typos and occasionally diverging in other ways on the C, Rust, Python, R, and Julia sides. But, I'm open to discussion of this strategy issue.

[ocefpaf]

To be honest I don't know the best approach here. I'm ok closing it and let this PR be just a documentation step for us and others using the Matlab version.

[ocefpaf]

@efiring I was thinking about this and I wonder. We do have the official release in the tags. We can keep latest main in sync with the latest official tag and maintain a branch, community (?), with the bug fixes, typos, etc, that can guide the community on what to do and hopefully get those upstream to the official release. I'm not sure if that is the best idea but many found this repo looking for a way to help out.