sh is bad at exiting on error

ci-tools/update-nixpkgs

 #!/usr/bin/env nix-shell
-#!nix-shell -i sh -p nixUnstable git openssh curl
+#!nix-shell -i bash -p nixUnstable git openssh curl
 
 # ^^
 # we get nixUnstable for the diff-closures command, mostly.