Add fallback when git is unavailable in TIA mode (Docker environments)

When enabling Pest V5's TIA (Test Impact Analysis) mode in a Dockerized application where the git binary is not installed, the process crashes with a MissingDependency exception: The feature "Tia mode" requires "git".

This prevents running tests with --tia flags in minimal Docker containers.

Reproduction

1. Create a Dockerfile without git (common in production images)
2. Install dependencies including Pest
3. Run ./vendor/bin/pest --tia
4. Observe error: The feature "Tia mode" requires "git".