This results in anything that uses nixpkgs getting stopped in the
debugger inside of nixpkgs internals, which are usually irrelevant.
Let's default to the more useful option.
Fixes: https://git.lix.systems/lix-project/lix/issues/666
Change-Id: If4b94a3d488bfb2f634ee5a2bc195e7a4b5434a5