escape?

.github/workflows/build.yml

@@ -22,7 +22,7 @@ jobs:
       - name: "Determine hosts"
         id: hosts
         run: |
-          hostnames="$(nix eval .#nixosConfigurations --apply builtins.attrNames --json)"
+          hostnames="$(nix eval .#nixosConfigurations --apply builtins.attrNames --json | tr '\n' ', ' | sed 's/,$//')"
           printf "hostnames=%s\n" "${hostnames}" >> "${GITHUB_OUTPUT}"
 
   build: