Add CPython 3.13 to test matrix

Author: oscarbenjamin

.github/workflows/buildwheel.yml

@@ -124,7 +124,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ['3.11', '3.12']
+        python-version: ['3.11', '3.12', '3.13-dev']
         # '.' means install from git checkout
         # 'python-flint' means install from PyPI sdist
         target: ['.', 'python-flint']