[cicd] add NIX_PATH to tests (#708)

## Summary

Testing this fix out (I can't remember if exported variables are
available across steps in GHA)

## How was it tested?

Testing in CICD

Author: mikeland73

.github/workflows/cli-tests.yaml

@@ -101,7 +101,9 @@ jobs:
           echo "NIX_PATH=$NIX_PATH" >> $GITHUB_ENV
           echo "PATH=$PATH" >> $GITHUB_ENV
       - name: Run tests
-        run: go test -race -cover -v ./...
+        run: |
+          export NIX_PATH=nixpkgs=https://github.com/nixos/nixpkgs/tarball/nixos-unstable
+          go test -race -cover -v ./...
 
   auto-nix-install: # ensure Devbox installs nix and works properly after installation.
     runs-on: ubuntu-latest