Update pytest from 6.2.2 to 6.2.3 (#532)

Author: pyup-bot

requirements-testing.txt

@@ -2,7 +2,7 @@ wheel==0.36.2
 python-coveralls==2.9.3
 coverage==5.5
 flake8==3.9.0
-pytest==6.2.2
+pytest==6.2.3
 pytest-cov==2.11.1
 autopep8==1.5.6
 mypy==0.812