fix: pin liteLLM upper bound to 1.82.6 to mitigate supply chain attack (openai#2772)

Author: gn00295120

pyproject.toml

@@ -36,7 +36,7 @@ Repository = "https://github.com/openai/openai-agents-python"
 [project.optional-dependencies]
 voice = ["numpy>=2.2.0, <3; python_version>='3.10'", "websockets>=15.0, <16"]
 viz = ["graphviz>=0.17"]
-litellm = ["litellm>=1.81.0, <2"]
+litellm = ["litellm>=1.81.0, <=1.82.6"]
 any-llm = ["any-llm-sdk>=1.11.0, <2; python_version >= '3.11'"]
 realtime = ["websockets>=15.0, <16"]
 sqlalchemy = ["SQLAlchemy>=2.0", "asyncpg>=0.29.0"]