It is a bit of a mess tbh; I think you are likely doing Pkg operations on the test environment (is that right?), and in that case, Pkg treats the stdlibs as v0.0.0 on many Julia versions, and therefore needs the compat to be ="<0.0.1, 1" for all stdlibs in your package AND all of your dependencies, recursively. That either means a ton of PRs to dependencies to loosen the bounds in that way, or to avoid doing any pkg operations on the test env. (Note it seems fine if you create a new env with Pkg.activate, add packages there, and then switch back).
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