Bump langchain from 0.0.304 to 0.0.312

Bumps [langchain](https://github.com/langchain-ai/langchain) from 0.0.304 to 0.0.312.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@v0.0.304...v0.0.312)

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

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