lookup: add pnpm

[GeoffreyBooth]

Split off from #1020.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.32%. Comparing base (46d35ae) to head (c2e4677).
Report is 47 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1027   +/-   ##
=======================================
  Coverage   96.32%   96.32%           
=======================================
  Files          28       28           
  Lines        2177     2177           
=======================================
  Hits         2097     2097           
  Misses         80       80           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[GeoffreyBooth]

The workflow that ran for this PR passed with a retry for v18 Windows, but didn’t run for 21 (?). When I run it manually I get failures: https://github.com/nodejs/citgm/actions/runs/6843202973/job/18605533429. Are the differing results due to flakiness or something about how the workflows are run?