Bump pypdf from 4.3.1 to 6.0.0 in /app/backend (#2674)

* Bump pypdf from 4.3.1 to 6.0.0 in /app/backend

Bumps [pypdf](https://github.com/py-pdf/pypdf) from 4.3.1 to 6.0.0.
- [Release notes](https://github.com/py-pdf/pypdf/releases)
- [Changelog](https://github.com/py-pdf/pypdf/blob/main/CHANGELOG.md)
- [Commits](py-pdf/pypdf@4.3.1...6.0.0)

---
updated-dependencies:
- dependency-name: pypdf
  dependency-version: 6.0.0
  dependency-type: direct:production
...

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* Update snapshot for splitting

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Pamela Fox <pamela.fox@gmail.com>

Author: dependabot[bot]

app/backend/requirements.txt

@@ -352,7 +352,7 @@ pyjwt[crypto]==2.10.1
     #   msal
 pymupdf==1.26.0
     # via -r requirements.in
-pypdf==4.3.1
+pypdf==6.0.0
     # via -r requirements.in
 python-dotenv==1.1.1
     # via