ci: Fix nix-parse workflow

The nix_path definition was missing :/

.github/workflows/nix-parse.yml

@@ -19,7 +19,7 @@ jobs:
       run: |
         gh api \
           repos/NixOS/nixpkgs/pulls/${{github.event.number}}/files --paginate \
-          | jq '.[] | select(.status != "removed" and (.filename | endswith(".nix"))) | .filename' \
+          | jq --raw-output '.[] | select(.status != "removed" and (.filename | endswith(".nix"))) | .filename' \
           > "$HOME/changed_files"
         if [[ -s "$HOME/changed_files" ]]; then
           echo "CHANGED_FILES=$HOME/changed_files" > "$GITHUB_ENV"
@@ -30,6 +30,8 @@ jobs:
         ref: refs/pull/${{ github.event.pull_request.number }}/merge
       if: ${{ env.CHANGED_FILES && env.CHANGED_FILES != '' }}
     - uses: cachix/install-nix-action@7ac1ec25491415c381d9b62f0657c7a028df52a7 # v24
+      with:
+        nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Parse all changed or added nix files
       run: |
         ret=0