bug#46297: nix-service-configuration is missing the default /bin/sh

[pukkamustard]

Oleg Pykhalov <go.wigust@gmail.com> writes:

[…]

> Could you apply the following patch on
> 13c4a377f5a2e1240790679f3d5643385b6d7635 and run the command 
> again,
> please?

Applied and tested in a virtual machine. Your patch seems to fix 
the issue I was having. Thank you!

Also tested again in a VM without your patches and was able to 
reproduce the error as reported.

For completeness the commands I ran in the VM:

```
$ nix-channel add https://nixos.org/channels/nixpkgs-unstable 
nixpkgs
$ nix-channel --update
$ nix-build '<nixpkgs>' -I .nix-defexpr/channels -A 
ocaml-ng.ocamlPackages_4_11.ocaml
/nix/store/gvwnh8wn0ib40fd6k3wa4xf7ja1y17l9-ocaml-4.11.2
```

-pukkamustard