Revert "all-packages.nix: Don't recurse into 'tests'", fix eval release.nix

This reverts commit 014c26d7.

recurseIntoAttrs is needed in order to evaluate the tests in release.nix.
See https://github.com/NixOS/nixpkgs/commit/014c26d75bb5323de7cc2c0399bf73cfd5d8a36b

cc @edolstra