CI speed improvements (#93411)
## What?
- Restore pnpm store for test timing fetch to speed up `pnpm install` in
that step.
- Skip playwright install when it's not needed. Multiple steps don't
need Playwright in order to run. Saves 41 seconds per step that doesn't
need it.
- Removed extra playwright install on the `test-firefox-safari` as
Playwright already gets installed in the reusable workflow.
### Before (canary)
<img width="1546" height="1142" alt="CleanShot 2026-05-01 at 16 17
37@2x"
src="https://github.com/user-attachments/assets/7819915b-9c42-4286-b0b9-c2489b322825"
/>
### After (This PR)
<img width="1588" height="968" alt="CleanShot 2026-05-01 at 16 17 25@2x"
src="https://github.com/user-attachments/assets/fb583831-a78c-42db-a77d-7e27af9c1f35"
/>
---------
Co-authored-by: Benjamin Woodruff <benjamin.woodruff@vercel.com>
