Bump langchain-community from 0.2.0 to 0.2.9 in /backend

Bumps [langchain-community](https://github.com/langchain-ai/langchain) from 0.2.0 to 0.2.9.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@langchain-community==0.2.0...langchain-community==0.2.9)

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

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

backend/requirements.txt

@@ -25,7 +25,7 @@ APScheduler==3.10.4
 google-generativeai==0.5.4
 
 langchain==0.2.0
-langchain-community==0.2.0
+langchain-community==0.2.9
 langchain-chroma==0.1.1
 
 fake-useragent==1.5.1