Add Python 3.13 (#47)

Author: fabaff

.github/workflows/testing.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [ "3.11", "3.12" ]
+        python-version: [ "3.11", "3.12", "3.13" ]
 
     steps:
     - name: Checkout