Patch pdfminer requirements for unstructured_data

Adds pdfminer.six==20231228 to src/retrievers/unstructured_data/requirements.txt in order to resolve dependency deployment bug

Author: stevenrick

src/retrievers/unstructured_data/requirements.txt

@@ -8,4 +8,5 @@ unstructured[all-docs]==0.12.5
 python-multipart==0.0.18
 langchain-community==0.3.0
 pymilvus==2.4.0
-sentence-transformers==3.0.0
+sentence-transformers==3.0.0
+pdfminer.six==20231228