Bump langchain from 0.0.305 to 0.0.308

Bumps [langchain](https://github.com/langchain-ai/langchain) from 0.0.305 to 0.0.308.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](https://github.com/langchain-ai/langchain/compare/v0.0.305...v0.0.308)

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

Signed-off-by: dependabot[bot] <[email protected]>

requirements.txt

@@ -1,6 +1,6 @@
 anthropic==0.3.11
 faiss-cpu==1.7.4
-langchain==0.0.305
+langchain==0.0.308
 langsmith==0.0.41
 numpy>=1.22.2 # not directly required, pinned by Snyk to avoid a vulnerability
 openai==0.28.1