Bump pytest from 8.4.2 to 9.0.0 in /backend (#2600)

Bumps [pytest](https://github.com/pytest-dev/pytest) from 8.4.2 to 9.0.0.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/main/CHANGELOG.rst)
- [Commits](pytest-dev/pytest@8.4.2...9.0.0)

---
updated-dependencies:
- dependency-name: pytest
  dependency-version: 9.0.0
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

backend/poetry.lock

@@ -55,7 +55,7 @@ pre-commit = "^4.1.0"
 ruff = "^0.14.2"
 
 [tool.poetry.group.test.dependencies]
-pytest = "^8.3.4"
+pytest = "^9.0.0"
 pytest-cov = "^7.0"
 pytest-django = "^4.5"
 pytest-mock = "^3.0"