Update pytest-xdist requirement from <3.0.0,>=1.28.0 to >=1.28.0,<4.0.0

Updates the requirements on [pytest-xdist](https://github.com/pytest-dev/pytest-xdist) to permit the latest version.
- [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@v1.28.0...v3.0.2)

---
updated-dependencies:
- dependency-name: pytest-xdist
  dependency-type: direct:development
...

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

Author: dependabot[bot]

requirements/dev.txt

@@ -6,7 +6,7 @@ types-requests>=2.25.0, <3.0.0
 # testing
 pytest>=5.3.5, <8.0.0
 pytest-cov>=2.6.1, <5.0.0
-pytest-xdist>=1.28.0, <3.0.0 # for distributed testing, currently unused (see setup.cfg)
+pytest-xdist>=1.28.0, <4.0.0 # for distributed testing, currently unused (see setup.cfg)
 pytest-lazy-fixture>=0.6.3, <0.7.0
 pytest-custom_exit_code>=0.3.0 # for notebook tests
 pytest-timeout>=1.4.2, <3.0.0 # for notebook tests