How do I update dependencies in Ruby development?

As advised in the manual, I’ve used bundix to install the dependencies of a Ruby project. Now I’d like to update them. Typically I’d review potential updates via:

bundle outdated

then update the lock file via:

bundle update

In this environment, however, the former fails with “you are trying to check outdated gems in deployment mode” and the latter fails by trying to actually install dependencies into the Nix store.

Updating dependencies is a pretty basic need, so I assume there’s a way to do this. How is it supposed to work?