deps: bump GitPython to 3.1.61

[katsugtgz]

Updates GitPython to address 22 reported advisories, including GHSA-2f96-g7mh-g2hx, GHSA-3f7w-8rr8-f37f, GHSA-4gmw-gg2m-w46p, GHSA-9rj7-rf2p-w77r, and GHSA-539m-9xh6-q6rr.

Evidence:

• requirements.txt and pyproject.toml pinned gitpython==3.1.45
• osv-scanner reported 22 advisories for gitpython@3.1.45 before the update
• updated version: 3.1.58

Validation:

• osv-scanner no longer reports any advisory for gitpython@3.1.58 after the update
• uv lock resolves cleanly; GitPython 3.1.58 imports and runs a basic repo init/commit against gitdb 4.0.12 (the pinned version)

Note: osv-scanner still reports advisories for other packages in this repo (for example torch in robomimic/requirements.txt with no pinned version). This patch only touches GitPython.

Scope: dependency/lockfile update only (requirements.txt, pyproject.toml, uv.lock).

[katsugtgz]

Rebased onto main and moved the pin to 3.1.61, since 3.1.58 is now covered by newer advisories (fixed in 3.1.59). osv-scanner reports no GitPython advisories at 3.1.61. Sorry for the churn.