Update unstructured requirement in /topic/machine-learning/llm-langchain

Updates the requirements on [unstructured](https://github.com/Unstructured-IO/unstructured) to permit the latest version.
- [Release notes](https://github.com/Unstructured-IO/unstructured/releases)
- [Changelog](https://github.com/Unstructured-IO/unstructured/blob/main/CHANGELOG.md)
- [Commits](Unstructured-IO/unstructured@0.2.0...0.18.1)

---
updated-dependencies:
- dependency-name: unstructured
  dependency-version: 0.18.1
  dependency-type: direct:production
...

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Author: dependabot[bot]

topic/machine-learning/llm-langchain/requirements.txt

@@ -9,4 +9,4 @@ pypdf<6
 python-dotenv<2
 requests<3
 requests-cache<2
-unstructured<0.18
+unstructured<0.19