Bump pytest-asyncio from 0.25.3 to 0.26.0 in /backend

Bumps [pytest-asyncio](https://github.com/pytest-dev/pytest-asyncio) from 0.25.3 to 0.26.0.
- [Release notes](https://github.com/pytest-dev/pytest-asyncio/releases)
- [Commits](pytest-dev/pytest-asyncio@v0.25.3...v0.26.0)

---
updated-dependencies:
- dependency-name: pytest-asyncio
  dependency-version: 0.26.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]