Bump langchain from 0.1.11 to 0.3.7 in /blog/pi

Bumps [langchain](https://github.com/langchain-ai/langchain) from 0.1.11 to 0.3.7.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@langchain-openai==0.1.11...langchain==0.3.7)

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

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

Author: dependabot[bot]