Add {sqlite,postgres} factor to tox envlist

Tox 4.54 rejects env names that aren't declared in envlist, so the CI
matrix was failing with "provided environments not found in
configuration file: py3.11-django5.2-wagtail7.0-sqlite". The GitHub
workflows pass TOXENV with a -sqlite or -postgres suffix to pick up the
psycopg2 factor-conditional dep, so add that factor to every envlist
entry.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: nickmoreton

tox.ini

@@ -2,9 +2,9 @@
 min_version = 4.11
 
 envlist =
-    py{3.11,3.12,3.13}-django5.2-wagtail7.0
-    py{3.11,3.12,3.13,3.14}-django5.2-wagtail7.4
-    py{3.13,3.14}-django6.0-wagtail7.4
+    py{3.11,3.12,3.13}-django5.2-wagtail7.0-{sqlite,postgres}
+    py{3.11,3.12,3.13,3.14}-django5.2-wagtail7.4-{sqlite,postgres}
+    py{3.13,3.14}-django6.0-wagtail7.4-{sqlite,postgres}
 
 [gh-actions]
 python =