Bump pypdf from 6.7.2 to 6.7.4 in /backend

Bumps [pypdf](https://github.com/py-pdf/pypdf) from 6.7.2 to 6.7.4.
- [Release notes](https://github.com/py-pdf/pypdf/releases)
- [Changelog](https://github.com/py-pdf/pypdf/blob/main/CHANGELOG.md)
- [Commits](py-pdf/pypdf@6.7.2...6.7.4)

---
updated-dependencies:
- dependency-name: pypdf
  dependency-version: 6.7.4
  dependency-type: direct:production
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -167,7 +167,7 @@ pyopenssl==24.2.1
     # via pysaml2
 pyparsing==3.2.5
     # via rdflib
-pypdf==6.7.2
+pypdf==6.7.4
     # via -r requirements.in
 pyreadr==0.5.4
     # via -r requirements.in