fix(CI): Reduce Rspack test retries from 2 to 0 to reduce timeouts (#78390)

Seeing a lot more timeouts recently for whatever reason. Reducing the test retries should hopefully mitigate this.
## Attempts with 1 retry:
https://github.com/vercel/next.js/actions/runs/14583128222
https://github.com/vercel/next.js/actions/runs/14583135455
Still has some timeouts 😞
## Attempts with no retries:
https://github.com/vercel/next.js/actions/runs/14586654389
https://github.com/vercel/next.js/actions/runs/14586656222