I did peer review for a number of scientific papers that include code. Almost every time, I was the only reviewer that even look at the code.

In most cases, peer reviewers will just assume that authors claiming the "code is available" means that a) it is reproducible and b) it is actually there.

As a counter example, this recent splashy paper

https://www.nature.com/articles/s41587-021-00907-6

claims the code is available on github, but the github version ( https://github.com/jameswweis/delphi ) contains the actual model only as a Pickle file, and contains no data or featurization.

So clearly, the peer reviewers didn't look at it.