Make 3.13 tests optional

Author: ezio-melotti

.github/workflows/test.yml

@@ -12,6 +12,9 @@ jobs:
       fail-fast: false
       matrix:
         python-version: ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13"]
+        include:
+          - python-version: "3.13"
+            continue-on-error: true
 
     steps:
       - uses: actions/checkout@v4