Test that CACHIX_AUTH_TOKEN is set to run pkg:nix:deploy.
Test that CACHIX_AUTH_TOKEN is set to run pkg:nix:deploy.

Coq is now a managed Cachix so this variable should be defined and we
check for its presence.

This will avoid failures when building on forks where this is not
defined.

SkySkimmer/coq,ejgallego/coq,coq/coq,ejgallego/coq,SkySkimmer/coq,coq/coq,coq/coq,ejgallego/coq,Zimmi48/coq,SkySkimmer/coq,ejgallego/coq,Zimmi48/coq,Zimmi48/coq,SkySkimmer/coq,coq/coq,Zimmi48/coq