chore: parse pack --json object output in node integration

[reggi]

Problem

The build nodejs jobs in Release Integration / publish fail at .github/workflows/node-integration.yml:

node . pack --loglevel=silent --json | jq -r .[0].filename
→ jq: error (at <stdin>:9859): Cannot index object with number
→ Process completed with exit code 5

As of #9247 (sync json output of pack and publish), npm pack --json no longer outputs an array. logTar now buffers { [tar.name]: tarball }, so the output is an object keyed by package name:

{ "npm": { "filename": "npm-12.0.1.tgz", ... } }

The workflow still parsed it with .[0].filename, which errors on an object. npm 12.0.x is the first release carrying this change, so the release integration only started breaking now.

Fix

Parse the filename from the object instead of an array index:

-npmtarball="$(node . pack --loglevel=silent --json | jq -r .[0].filename)"
+npmtarball="$(node . pack --loglevel=silent --json | jq -r 'to_entries[0].value.filename')"

Verified locally: returns npm-12.0.1.tgz.