deps: update pytest-xdist requirement from >=3.0 to >=3.8.0

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@v3.0.0...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

@@ -90,7 +90,7 @@ learned = [
 ]
 dev = [
     "pytest>=7.0",
-    "pytest-xdist>=3.0",
+    "pytest-xdist>=3.8.0",
     # pytest-asyncio is required by tests/test_taint_classifier.py — those
     # tests use ``@pytest.mark.asyncio`` to verify the MCP-sampling-based
     # taint classifier under a controlled async loop.