chore(deps): bump langchain from 0.2.5 to 0.2.6

Bumps [langchain](https://github.com/langchain-ai/langchain) from 0.2.5 to 0.2.6.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@langchain==0.2.5...langchain==0.2.6)

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

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

requirements.txt

@@ -20,7 +20,7 @@ codespell==2.3.0
 # production
 # ------------
 python-decouple==3.8
-langchain==0.2.5
+langchain==0.2.6
 langchainhub==0.1.20
 langchain-openai==0.1.13
 langchain-pinecone==0.1.1