Sort imports

Using pytest's style.

testing/test_plugin.py

@@ -1,13 +1,13 @@
 from contextlib import suppress
+import os
 from pathlib import Path
 import sys
-import os
 
 import execnet
-from xdist.workermanage import NodeManager
-
 import pytest
 
+from xdist.workermanage import NodeManager
+
 
 @pytest.fixture
 def monkeypatch_3_cpus(monkeypatch: pytest.MonkeyPatch):