chore(deps): bump langchain

Bumps [langchain](https://github.com/langchain-ai/langchain) from 0.3.27 to 0.3.30.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@langchain==0.3.27...langchain==0.3.30)

---
updated-dependencies:
- dependency-name: langchain
  dependency-version: 0.3.30
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

python/assistant-transport-backend-langgraph/pyproject.toml

@@ -11,7 +11,7 @@ dependencies = [
     "pydantic>=2.0.0",
     "python-dotenv>=1.0.0",
     "langgraph>=0.2.0",
-    "langchain>=0.2.0",
+    "langchain>=0.3.30",
     "langchain-core>=0.2.0",
     "langchain-openai>=0.1.0",
     "httpx>=0.24.0",

python/assistant-transport-backend-langgraph/requirements.txt

@@ -7,7 +7,7 @@ python-dotenv>=1.0.0
 
 # LangGraph dependencies
 langgraph>=0.2.0
-langchain>=0.2.0
+langchain>=0.3.30
 langchain-core>=0.2.0
 langchain-openai>=0.1.0