[ci] Added Django 6.0 to CI test matrix

Author: nemesifier

.github/workflows/ci.yml

@@ -32,6 +32,7 @@ jobs:
           - django~=5.0.0
           - django~=5.1.0
           - django~=5.2.0
+          - django~=6.0.0
         exclude:
           # Python 3.13 supported only in Django >=5.1.3
           - python-version: "3.13"