nix/review_shell.nix: use ignoreFileOutputs whenever available

[ShamrockLee]

This PR depends on NixOS/nixpkgs#353752 and fixes #408 partially.

Cc: @corngood

[Mic92]

Thanks. Looks good.

[ShamrockLee]

Considering that the single-file-output error is a potential way to enforce the correctness of meta.outputsToInstall, we may want to preserve such behavior while proving options to ignore those single-file outputs.

I prepared the implementation to support nixpkgs-review --ignore-single-file-outputs locally. I could push it up if we agree that this should be supported through a flag.

@Mic92, what do you think?