Cost freezing take 3 (#67)

Author: ca16

pyproject.toml

@@ -13,7 +13,7 @@ dependencies = [
   "inspect-ai>=0.3.104",
   # pin litellm so that we know what model costs we're using
   # see the Development.md doc before changing
-  "litellm==1.67.4.post1",
+  "litellm>=1.67.4.post1,<=1.75.8",
   "pydantic>=2.0.0",
   # For leaderboard
   "huggingface_hub",