Revert "Bump pytest-xdist from 2.4.0 to 3.6.1"

setup.cfg

@@ -109,7 +109,7 @@ dev =
     pytest              == 6.2.5   # Testing
     pytest-cov          == 2.12.1  # pytest + coverage = pytest-cov
     pytest-watch        == 4.2.0   # Automatic testing every time you save a file
-    pytest-xdist        == 3.6.1   # You got multiple cores, right?
+    pytest-xdist        == 2.4.0   # You got multiple cores, right?
     pre-commit          == 2.15.0  # Auto-run checks on every commit
     tox                 ~= 4.11.0  # A way to automate and standardize testing in Python
     types-requests      ~= 2.31.0.20240218