Restrict the test matrix by Django version

tox.ini

@@ -1,9 +1,14 @@
 [tox]
 isolated_build = True
 envlist =
-    py{38,39}-django{32,40,41,main}-{postgres,mysql,sqlite}
-    py310-django{32,40,41,main}-{postgres,mysql,sqlite}
-    py311-django{41,main}-{postgres,mysql,sqlite}
+    # Django 3.2 LTS. Limited support matrix.
+    django32-py{38,39,310}-{postgres,mysql}
+    # Django 4.0
+    django40-py{38,39,310}-{postgres,mysql,sqlite}
+    # Django 4.1
+    django41-py{38,39,310}-{postgres,mysql,sqlite}
+    # Django mainline - Only test on latest python / postgres
+    djangomain-py311-postgres
 
 skip_missing_interpreters = True