Fix pnpm workspace change detection in VS Code publish workflow - W-24490676

[peternhale]

Summary

Install the VS Code change-detector tools in a temporary directory outside the consumer repository. Run tsx from that directory while keeping the consumer checkout as the working directory.

The current npm install --no-save runs inside pnpm workspaces and fails on workspace:* dependencies before change detection starts. This affected the Apex LS nightly release. The change leaves npm, Yarn, and pnpm caller inputs unchanged.

Validation

• Ran the isolated install and change detector from the Apex LS pnpm workspace; it found the VS Code extension and completed.
• Ran the same flow against a temporary npm consumer; it completed.
• Parsed the workflow YAML and ran git diff --check.

Work item: W-24490676
Related Apex LS PR: forcedotcom/apex-language-support#746