Fix yarn install in CI now that Varbase Project 11.0.x-dev ships no yarn.lock

Problem/Motivation

The 2.0.x "Automated Functional Testing" job runs yarn install in .site, a Varbase Project 11.0.x-dev checkout. Varbase Project no longer ships a yarn.lock (Back to DEV in #3629850: Plan: release Varbase Project 11.0.11), so Yarn takes this recipe's own package.json as the project root and stops with a Usage Error.

The last 2.0.x pipeline ran on 5 October 2026, before that change, so it is still green. The same setup already fails on varbase_events_base (#3630029: Fix yarn install in CI now that Varbase Project 11.0.x-dev ships no yarn.lock).

Steps to reproduce

Run the 2.0.x pipeline. The same failure on varbase_events_base: job 12789375.

Proposed resolution

Create an empty yarn.lock in .site before yarn install, as Yarn suggests, so the test site is its own Yarn project.

Remaining tasks

• ✅ File an issue
• ❌ Addition/Change/Update/Fix
• ❌ Testing to ensure no regression
• ➖ Automated unit/functional testing coverage
• ➖ Developer Documentation support
• ➖ User Guide Documentation support
• ➖ UX/UI designer responsibilities
• ➖ Accessibility and Readability
• ❌ Reviewed by a human
• ❌ Code review by maintainers
• ❌ Full testing and approval
• ❌ Credit contributors
• ❌ Review with the product owner
• ❌ Update Release Notes
• ❌ Release

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• N/A