Bump langchain in /End_to_end_Solutions/AOAISearchDemo/app

Bumps [langchain](https://github.com/hwchase17/langchain) from 0.0.139 to 0.0.236.
- [Release notes](https://github.com/hwchase17/langchain/releases)
- [Commits](langchain-ai/langchain@v0.0.139...v0.0.236)

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

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

End_to_end_Solutions/AOAISearchDemo/app/requirements.txt

@@ -1,6 +1,6 @@
 azure-identity==1.13.0b3
 Flask==2.2.2
-langchain==0.0.139
+langchain==0.0.236
 openai==0.27.4
 azure-search-documents==11.4.0b3
 azure-storage-blob==12.14.1