Demo of how the go command behaves when the same package is is two modules, one nested inside the other, at the same version.
github.com/jba/nested-modules@v1.0.0 is a module with a package in directory inner.
github.com/jba/nested-modules/inner@v1.0.0 is a module with a package at the root.
What does go get github.com/jba/nested-modules/inner@v1.0.0 do?