chore(deps): bump pypdf from 6.13.0 to 6.13.3 in /src/backend

Bumps [pypdf](https://github.com/py-pdf/pypdf) from 6.13.0 to 6.13.3.
- [Release notes](https://github.com/py-pdf/pypdf/releases)
- [Changelog](https://github.com/py-pdf/pypdf/blob/main/CHANGELOG.md)
- [Commits](https://github.com/py-pdf/pypdf/compare/6.13.0...6.13.3)

---
updated-dependencies:
- dependency-name: pypdf
  dependency-version: 6.13.3
  dependency-type: direct:production
...

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

src/backend/requirements-3.14.txt

@@ -1707,9 +1707,9 @@ pynacl==1.6.2 \
     # via
     #   -c src/backend/requirements.txt
     #   paramiko
-pypdf==6.13.0 \
-    --hash=sha256:558683ec9daf6b91c280c322c84c32f5cc216afd3eaa3a37de5ae88ae0c3b787 \
-    --hash=sha256:de1294ae49d6956edb4e5c41527fb9e8716ddd2b120f2185c68aab784d4ffe60
+pypdf==6.13.3 \
+    --hash=sha256:c6e3f86afb625791510b02ad5480e94b63970bb957df75d44657c282ecc52224 \
+    --hash=sha256:f3cb822769725f1bac658c406cfc9460399043f3750c2d3e4650e0a85eacabd7
     # via
     #   -c src/backend/requirements.txt
     #   -r src/backend/requirements.in