Merge from develop to production

... to fix the weekly nixpkgs update script.

ci-tools/update-nixpkgs

 #!/usr/bin/env nix-shell
-#!nix-shell -i bash -p nixUnstable git curl python3
+#!nix-shell -i bash -p git curl python3
 
 # ^^
-# we get nixUnstable for the diff-closures command, mostly.
 # we need git to commit and push our changes
 # we need curl to create the gitlab MR
 # we need python to format the data as json