Add conditional check for git checkout in development path

[KJ7LNW]

This PR adds a conditional check to only insert the development path into sys.path when running from a git checkout.

Changes

• Added entire conditional block with os.path.exists() check for ../.git directory
• Wrapped the existing sys.path.insert() call in the new conditional
• Previously the development path was always inserted - now it only happens when running from a git repository

Benefits

• More robust: Prevents potential import errors when script is run from installed package
• Cleaner behavior: Only modifies sys.path when actually in a development environment
• Production-safe: Falls back gracefully to installed package in non-git environments

Usage

When running from a git checkout:

./bin/github-backup --help

The script will detect the .git directory and use the development tree.

When running from an installed package, it will use the installed modules without attempting to modify sys.path.

Before: The sys.path.insert() was always executed
After: The sys.path.insert() only executes when ../.git exists