build(deps): bump langchain from 0.0.331 to 0.2.1

Bumps [langchain](https://github.com/langchain-ai/langchain) from 0.0.331 to 0.2.1.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@v0.0.331...langchain==0.2.1)

---
updated-dependencies:
- dependency-name: langchain
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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