Use 'tested' aggregate job

What we were doing before was slightly incorrect. We'd upload AMIs
for NixOS evals that wouldn't end up as channel bumps.

By using the 'tested' job (like https://status.nixos.org) we actually
upload the correct thing

.github/workflows/upload-legacy-ami.yml

@@ -36,7 +36,8 @@ jobs:
         id: download_ami
         run: |
           set -o pipefail
-          out=$(curl --location --silent --fail-with-body --header 'Accept: application/json' https://hydra.nixos.org/job/nixos/${{ matrix.release }}/nixos.amazonImage.${{ matrix.system }}/latest-finished  | jq --raw-output '.buildoutputs.out.path')
+          build_id=$(curl -sSL -H 'Accept: application/json https://hydra.nixos.org/job/nixos/${{ matrix.release }}/tested/latest-finished | jq -r '.id')
+          out=$(curl -sSL -H 'Accept: application/json' https://hydra.nixos.org/build/${build_id}/constituents  | jq -r '.[] | select(.job == "nixos.amazonImage.${{ matrix.system }}") | .buildoutputs.out.path')
           nix-store --realise "$out" --add-root ./result
           echo "image_info=$out/nix-support/image-info.json" >> "$GITHUB_OUTPUT"