Bump pytest-xdist from 2.1.0 to 2.2.0

Bumps [pytest-xdist](https://github.com/pytest-dev/pytest-xdist) from 2.1.0 to 2.2.0.
- [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@v2.1.0...v2.2.0)

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

requirements-test.txt

@@ -4,7 +4,7 @@ port-for==0.4
 pytest==6.2.0
 pytest-cov==2.10.1
 coverage==5.3 # pytest-cov
-pytest-xdist==2.1.0
+pytest-xdist==2.2.0
 Mock==4.0.3
 redis==3.5.3
 -e .[tests]