build(deps-dev): update pytest-xdist requirement

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@v1.15.0...v3.8.0)

---
updated-dependencies:
- dependency-name: pytest-xdist
  dependency-version: 3.8.0
  dependency-type: direct:development
...

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

Author: dependabot[bot]

pyproject.toml

@@ -47,7 +47,7 @@ dev = [
   "mock>=4.0.3,<5.0.0",
   "pytest-cov>=2.4,<3.0",
   "ruff>=0.14.0,<1.0.0",
-  "pytest-xdist>=1.15,<2.0",
+  "pytest-xdist>=1.15,<4.0",
   "respx>=0.20.0,<0.21.0; python_version=='3.7'",
   "respx>=0.22.0,<0.23.0; python_version>='3.8'",
   "importlib-metadata>=4.12,<5.0",