build(deps-dev): bump pytest-httpx from 0.30.0 to 0.31.1 in /backend

Bumps [pytest-httpx](https://github.com/Colin-b/pytest_httpx) from 0.30.0 to 0.31.1.
- [Release notes](https://github.com/Colin-b/pytest_httpx/releases)
- [Changelog](https://github.com/Colin-b/pytest_httpx/blob/develop/CHANGELOG.md)
- [Commits](Colin-b/pytest_httpx@v0.30.0...v0.31.1)

---
updated-dependencies:
- dependency-name: pytest-httpx
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>