ci: try to set NIX_PATH

Author: thomasjm

.github/workflows/ci.yml

@@ -40,11 +40,13 @@ jobs:
     - name: Build
       run: |
         # stack build --system-ghc --test --bench --no-run-tests --no-run-benchmarks
+        export NIX_PATH="nixpkgs=$(nix run .#nixpkgsPath)"
         nix run .#stack -- build --nix --test --bench --no-run-tests --no-run-benchmarks
 
     - name: Test
       run: |
         # stack test --system-ghc --test-arguments --print
+        export NIX_PATH="nixpkgs=$(nix run .#nixpkgsPath)"
         nix run .#stack -- test --nix --test-arguments --print
 
   no-gmp:

flake.nix

@@ -74,11 +74,11 @@
 
               exit 0
             '';
+
+            nixpkgsPath = pkgs.writeShellScriptBin "nixpkgsPath.sh" "echo -n ${pkgs.path}";
           });
 
           inherit flake;
-
-          nixpkgsPath = pkgs.path;
         }
     );