fixup! patch 2

Ref: pytest-dev/pytest#6925
Ref: pytest-dev/pytest-xdist#515

tox.ini

@@ -12,8 +12,8 @@ isolated_build = true
 isolated_build = true
 usedevelop = false
 deps =
-    pytest; python_version != "3.5"
-    pytest<5.4; python_version == "3.5"
+    pytest; python_version != "3.5" or system_platform != "darwin"
+    pytest<5.4; python_version == "3.5" and system_platform == "darwin"
     pytest-xdist
 commands =
     {envpython} -m pytest {posargs:}