Bump pypdf from 4.0.1 to 6.4.0

Bumps [pypdf](https://github.com/py-pdf/pypdf) from 4.0.1 to 6.4.0.
- [Release notes](https://github.com/py-pdf/pypdf/releases)
- [Changelog](https://github.com/py-pdf/pypdf/blob/main/CHANGELOG.md)
- [Commits](py-pdf/pypdf@4.0.1...6.4.0)

---
updated-dependencies:
- dependency-name: pypdf
  dependency-version: 6.4.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements.txt

@@ -1,5 +1,5 @@
 pyttsx3==2.98
-pypdf==4.0.1
+pypdf==6.4.0
 ebooklib==0.19
 beautifulsoup4==4.13.4
 html2text==2025.4.15