Update unstructured requirement from ^0.13.0 to >=0.13,<0.16

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@0.13.0...0.15.5)

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

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

pyproject.toml

@@ -36,7 +36,7 @@ mistune = "^3.0.2"
 htmldocx = "^0.0.6"
 python-docx = "^1.1.0"
 lxml = { version = ">=4.9.2", extras = ["html_clean"] }
-unstructured = "^0.13.0"
+unstructured = ">=0.13,<0.16"
 tiktoken = ">=0.7.0"
 
 [build-system]