Optimize cloning for PR stats (#50859)
Follow-up to https://github.com/vercel/next.js/pull/50853 this optimizes
how we clone the branches for generating stats.
Before:
https://github.com/vercel/next.js/actions/runs/5191059058/jobs/9358459062
21min
After:
https://github.com/vercel/next.js/actions/runs/5191282140/jobs/9358934393?pr=50859
11min
