ci(github-actions): add "3.13-dev" to Python tests (#1145)

Author: jakob-keller

.github/workflows/pythonpackage.yml

@@ -6,7 +6,7 @@ jobs:
   python-check:
     strategy:
       matrix:
-        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
+        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13-dev"]
         platform: [ubuntu-20.04, macos-latest, windows-latest]
     runs-on: ${{ matrix.platform }}
     steps: