Fix pytest not being installed in several PyPy tox environment

Author: althonos

setup.cfg

@@ -140,10 +140,10 @@ commands = python -m coverage run --rcfile {toxinidir}/setup.cfg -m pytest {posa
 deps =
   -rtests/requirements.txt
   coverage~=5.0
-  py{35,36,37,38,39}: pytest~=6.0
-  py{27,34}: pytest~=4.6
-  py{35,36,37,38,39}: pytest-randomly~=3.5
-  py{27,34}: pytest-randomly~=1.2
+  py{35,36,37,38,39,py36,py37}: pytest~=6.0
+  py{27,34,py27}: pytest~=4.6
+  py{35,36,37,38,39,py36,py37}: pytest-randomly~=3.5
+  py{27,34,py27}: pytest-randomly~=1.2
   scandir: .[scandir]
   !scandir: .