Bump pytest from 5.4.3 to 6.1.1 (#582)

Author: dependabot[bot]

requirements/requirements_dev.txt

@@ -10,7 +10,7 @@ hypothesis==4.53.1
 placebo==0.9.0
 pre-commit==2.6.0
 pylint==2.5.3
-pytest==5.4.3
+pytest==6.1.1
 pytest-black==0.3.10
 pytest-cov==2.10.0
 pytest-datadir==1.3.1