Bump langchain in /functions/most_popular_repo_langchain

Bumps [langchain](https://github.com/langchain-ai/langchain) from 0.2.15 to 0.3.1.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@langchain==0.2.15...langchain==0.3.1)

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

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

Author: dependabot[bot]

functions/most_popular_repo_langchain/requirements.txt

@@ -1,4 +1,4 @@
-langchain==0.2.15
+langchain==0.3.1
 langchain-community==0.2.15
 requests==2.32.3
 PyGithub==2.4.0