Bump pytest-xdist from 3.1.0 to 3.2.0 in /requirements (AtsushiSakai#793)

Bumps [pytest-xdist](https://github.com/pytest-dev/pytest-xdist) from 3.1.0 to 3.2.0.
- [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@v3.1.0...v3.2.0)

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

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

Author: dependabot[bot]

requirements/requirements.txt

@@ -3,6 +3,6 @@ scipy == 1.10.0
 matplotlib == 3.6.3
 cvxpy == 1.3.0
 pytest == 7.2.1 # For unit test
-pytest-xdist == 3.1.0 # For unit test
+pytest-xdist == 3.2.0 # For unit test
 mypy == 1.0.0 # For unit test
 ruff == 0.0.246 # For unit test