Add Python 3.13 CI build

Author: offa

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python: [ "3.8", "3.9", "3.10", "3.11", "3.12" ]
+        python: [ "3.8", "3.9", "3.10", "3.11", "3.12", "3.13" ]
     name: python-${{ matrix.python }}
     steps:
       - name: Checkout