build(deps-dev): bump pytest-xdist from 3.5.0 to 3.6.1 in /backend

Bumps [pytest-xdist](https://github.com/pytest-dev/pytest-xdist) from 3.5.0 to 3.6.1.
- [Release notes](https://github.com/pytest-dev/pytest-xdist/releases)
- [Changelog](https://github.com/pytest-dev/pytest-xdist/blob/master/CHANGELOG.rst)
- [Commits](pytest-dev/pytest-xdist@v3.5.0...v3.6.1)

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

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