Update tox.ini for Django 3.2, pypy, gh

* Specify how to install Django 3.2. These tests are currently running
  against later Django versions.
* Add basepython entries for pypy. This fixes running tox locally.
* Fix the cpython version mapping in [gh-actions]. The github action
  tests for cpython versions are running against the latest Django,
  instead of the set of possible Django versions.

tox.ini

@@ -32,10 +32,13 @@ basepython =
     3.10: python3.10
     3.11: python3.11
     3.12: python3.12
-    pypy3: pypy3
+    pypy38: pypy3.8
+    pypy39: pypy3.9
+    pypy310: pypy3.10
 
 deps =
     pytest
+    3.2.x: Django>=3.2,<3.3
     4.2.x: Django>=4.2,<4.3
     5.0.x: Django>=5.0.1,<5.1
     main: https://github.com/django/django/archive/main.tar.gz
@@ -45,11 +48,11 @@ deps =
 # Running tox in GHA without redefining it all in a GHA matrix:
 # https://github.com/ymyzk/tox-gh-actions
 python =
-    3.8: py38
-    3.9: py39
-    3.10: py310
-    3.11: py311
-    3.12: py312
+    3.8: 3.8
+    3.9: 3.9
+    3.10: 3.10
+    3.11: 3.11
+    3.12: 3.12
     pypy-3.8: pypy38
     pypy-3.9: pypy39
     pypy-3.10: pypy310