restore py39: python3.9

Reverts: I78a50c3bf7f460e29c1a31c3f8c544a7026ca830
Partially reverts: I2640dd17f62d5d40b54d8e5cf1279661d094e302

Change-Id: Ia1cda8064b4c938a9c58bdf3f5111f31c7b40c80

tox.ini

@@ -14,11 +14,10 @@ envlist =
 generate_user_files = -W error::UserWarning -m pwb generate_user_files -family:wikipedia -lang:test -v
 
 [testenv]
-# pypy3 bases on Python 3.9
 basepython =
     py37: python3.7
     py38: python3.8
-    py39: pypy3
+    py39: python3.9
     py310: python3.10
     py311: python3.11
     py312: python3.12
@@ -34,8 +33,8 @@ commands =
 
     hacking: flake8 --version
     hacking-py37: flake8 --format=default {posargs}
-    hacking-py39: flake8 --color always {posargs}
     hacking-py312: flake8 --color always {posargs}
+    hacking-pypy: flake8 --color always {posargs}
 
     deeptest: python {[params]generate_user_files}
     deeptest-py37: python -m unittest discover -vv -p "*_tests.py"