Update dependency pytest to v6

Author: renovate-bot

requirements.txt

@@ -9,7 +9,7 @@ packaging==20.4
 pluggy==0.13.1
 py==1.8.1
 pyparsing==2.4.7
-pytest==5.4.3
+pytest==6.0.1
 requests==2.23.0
 six==1.15.0
 soupsieve==2.0.1