Fix packages.ekg issue.

Author: hamishmack

flake.nix

@@ -9,7 +9,7 @@
       inputs.hackage.follows = "hackageNix";
     };
     hackageNix = {
-      url = "github:input-output-hk/hackage.nix";
+      url = "github:input-output-hk/hackage.nix?ref=for-stackage";
       flake = false;
     };
     iohkNix = {
@@ -213,6 +213,7 @@
 
             modules = [
               ({ lib, pkgs, ... }: {
+                package-keys = ["ekg"];
                 # Ignore version bounds
                 packages.katip.doExactConfig = true;
                 # Split data to reduce closure size