fix(actions): enable parallel cache uploads

Signed-off-by: Cameron Smith <cameron.ray.smith@gmail.com>

.github/actions/build_nix_image/action.yml

@@ -82,6 +82,7 @@ runs:
         substituters: "${{ inputs.nixSubstituterName }}"
         secret_keys: "${{ inputs.nixPrivateKey }}"
         use_nixcached: true
+        nixcached_upload_options: --jobs 8 --debug
 
     - name: Set GitHub CI Slug Variables
       uses: rlespinasse/github-slug-action@797d68864753cbceedc271349d402da4590e6302 # ratchet:rlespinasse/github-slug-action@v4