build: enable pdfminer.six dependency

- Uncomment pdfminer.six in requirements.txt
- Specify version 20231228 for pdfminer.six

requirements.txt

@@ -9,5 +9,5 @@ PyMuPDF>=1.24.9
 scikit-learn>=1.0.2
 torch>=2.2.2
 transformers
-# pdfminer.six==20231228
+pdfminer.six==20231228
 # The requirements.txt must ensure that only necessary external dependencies are introduced. If there are new dependencies to add, please contact the project administrator.