Bump langchain from 0.1.37 to 0.2.19

Bumps [langchain](https://github.com/langchain-ai/langchainjs) from 0.1.37 to 0.2.19.
- [Release notes](https://github.com/langchain-ai/langchainjs/releases)
- [Changelog](https://github.com/langchain-ai/langchainjs/blob/main/release_workspace.js)
- [Commits](langchain-ai/langchainjs@0.1.37...0.2.19)

---
updated-dependencies:
- dependency-name: langchain
  dependency-version: 0.2.19
  dependency-type: direct:production
...

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

Author: dependabot[bot]