build: bump langchain from 0.3.13 to 0.3.19

Bumps [langchain](https://github.com/langchain-ai/langchain) from 0.3.13 to 0.3.19.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@langchain==0.3.13...langchain==0.3.19)

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

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

Author: dependabot[bot]

requirements-dev.txt

@@ -4,7 +4,7 @@ Markdown==3.4.4
 requests==2.32.3
 tqdm==4.67.1
 tiktoken
-langchain==0.3.13
+langchain==0.3.19
 bs4==0.0.1
 urllib3==2.3.0
 pytest==8.3.4