Bump cryptography from 46.0.7 to 48.0.0 in /backend (#739)

Bumps [cryptography](https://github.com/pyca/cryptography) from 46.0.7 to 48.0.0.
- [Changelog](https://github.com/pyca/cryptography/blob/main/CHANGELOG.rst)
- [Commits](pyca/cryptography@46.0.7...48.0.0)

---
updated-dependencies:
- dependency-name: cryptography
  dependency-version: 47.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

backend/pyproject.toml

@@ -6,7 +6,7 @@ description = "A tool to help NGOs with managing the redirection of people's tax
 requires-python = ">=3.13"
 dependencies = [
   "blessed~=1.39.0",
-  "cryptography~=46.0.0",
+  "cryptography~=48.0.0",
   "django~=5.2.0",
   "django-allauth~=65.16.0",
   "django-auditlog~=3.4.0",