Add Python 3.13 to CI test matrix

Update .github/workflows/tests.yml to include Python 3.13 in the GitHub Actions matrix so the test suite runs against the latest Python release and verifies compatibility with 3.13.

Author: JR-1991

.github/workflows/tests.yml

@@ -6,7 +6,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.10", "3.11", "3.12"]
+        python-version: ["3.10", "3.11", "3.12", "3.13"]
     name: Test pyDataverse
     env:
       PORT: 8080