Build(deps): Bump pypdf from 6.0.0 to 6.4.0 in /backend in the pip group across 1 directory (#196)

Build(deps): Bump pypdf in /backend in the pip group across 1 directory

Bumps the pip group with 1 update in the /backend directory: [pypdf](https://github.com/py-pdf/pypdf).


Updates `pypdf` from 6.0.0 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@6.0.0...6.4.0)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

backend/pyproject.toml

@@ -27,7 +27,7 @@ dependencies = [
     "openai==1.100.2",
     "psycopg2-binary>=2.9.11",
     "pydantic>=2.11.7",
-    "pypdf==6.0.0",
+    "pypdf==6.4.0",
     "rank-bm25==0.2.2",
     "rich>=13.7.0",
     "sentence-transformers>=5.1.0",