ci: fix PR workflow names

[SchahinRohani]

Summary

Fix PR workflow check names so package test jobs render cleanly for both changed and unchanged package paths.

Changes

• Resolve package test targets directly in the detect job
• Add a none fallback matrix entry when no package-specific tests are required
• Render Nothing to test for PRs without package-specific test changes
• Preserve dynamic check names such as Tests / astro-bun when package tests run

Checklist

• Single-purpose PR (one concern, one PR)
• Linked issue (if applicable): #