Remove py2 pip warning message

tox.ini

@@ -24,10 +24,10 @@ deps =
 
 [testenv]
 passenv = DISPLAY XAUTHORITY
+setenv = PYTHONWARNINGS=ignore:DEPRECATION::pip._internal.cli.base_command
 deps=
     {[base]deps}
     pytest-cov
-    pytest-xdist
     h5py
     pyside2_512: pyside2>=5.12,<5.13
     pyqt5_512: pyqt5>=5.12,<5.13
@@ -46,4 +46,4 @@ conda_channels=
 
 commands=
     python -c "import pyqtgraph as pg; pg.systemInfo()"
-    pytest {posargs:.} 
+    pytest {posargs:}