chore: Pin litellm dependency to versions below 1.81.0

Update the litellm version constraint in both project dependencies and dev dependencies to exclude versions 1.81.0 and higher because unit test breakages in GitHub actions introduced by it.

This is a stopgap before the actual fix is added. Close #4225

Co-authored-by: Liang Wu <wuliang@google.com>
PiperOrigin-RevId: 859239880

Author: wuliang229

pyproject.toml

@@ -123,7 +123,7 @@ test = [
   "kubernetes>=29.0.0",                           # For GkeCodeExecutor
   "langchain-community>=0.3.17",
   "langgraph>=0.2.60, <0.4.8",                    # For LangGraphAgent
-  "litellm>=1.75.5, <2.0.0",                      # For LiteLLM tests
+  "litellm>=1.75.5, <1.81.0",                     # For LiteLLM tests
   "llama-index-readers-file>=0.4.0",              # For retrieval tests
   "openai>=1.100.2",                              # For LiteLLM
   "pytest-asyncio>=0.25.0",
@@ -153,7 +153,7 @@ extensions = [
   "docker>=7.0.0",                              # For ContainerCodeExecutor
   "kubernetes>=29.0.0",                         # For GkeCodeExecutor
   "langgraph>=0.2.60, <0.4.8",                  # For LangGraphAgent
-  "litellm>=1.75.5",                            # For LiteLlm class. Currently has OpenAI limitations. TODO: once LiteLlm fix it
+  "litellm>=1.75.5, <1.81.0",                   # For LiteLlm class. Currently has OpenAI limitations. TODO: once LiteLlm fix it
   "llama-index-readers-file>=0.4.0",            # For retrieval using LlamaIndex.
   "llama-index-embeddings-google-genai>=0.3.0", # For files retrieval using LlamaIndex.
   "lxml>=5.3.0",                                # For load_web_page tool.