tests: add py3.13 tests

Author: fsbraun

.github/workflows/codecov.yml

@@ -16,7 +16,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.9", "3.10", "3.11", "3.12"]  # latest release minus two
+        python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]  # latest release minus two
         requirements-file: [
             dj42_cms311.txt,
             dj42_cms41.txt,
@@ -38,6 +38,8 @@ jobs:
             requirements-file: dj52_cms50.txt
           - python-version: "3.12"
             requirements-file: dj42_cms311.txt
+          - python-version: "3.13"
+            requirements-file: dj42_cms311.txt
 
     steps:
     - uses: actions/checkout@v4