Fix stale credentials when fetching cached git repositories

Changes

Fixes two issues with git fetching:

1. Stale credentials: Credentials embedded in URLs were not being passed to fetch/clone operations on cached repositories, causing authentication failures when tokens rotate.

2. Stale content fallback: Removed graceful fallback to cached content on network errors, which could serve outdated Functions.

Reference

Step Runner cache not updating on Windows (#337 - closed)