TMP: CI: test using CPython 3.13

Author: johnyf

.github/workflows/main.yml

@@ -15,6 +15,7 @@ jobs:
                 python-version: [
                     '3.11',
                     '3.12',
+                    '3.13.0-rc.2',
                     ]
         steps:
             - uses: actions/checkout@v4