Dependency hardening: pin minimum safe dependency versions

Hi, thanks for PocketFlow-Tutorial-Codebase-Knowledge. Low-priority dependency-hardening note, not an active vulnerability report - a default install resolves to safe versions today.

These declarations also permit older versions with known CVEs; pinning a minimum prevents an accidental downgrade (please test compatibility):

• gitpython: pin >= 3.1.33 (e.g. CVE-2023-40590)
• requests: pin >= 2.32.4 (e.g. CVE-2023-32681 and 2 more)

(Low-priority dependency-hygiene note - feel free to close if not useful, happy to send a PR.)