Add free threaded python to build matrix

Author: Rowlando13

.github/workflows/tests.yaml

@@ -13,10 +13,11 @@ jobs:
       fail-fast: false
       matrix:
         include:
+          - {name: free-threaded, python: '3.13t'}
           - {python: '3.13'}
+          - {name: Windows, python: '3.13', os: windows-latest}
+          - {name: Mac, python: '3.13', os: macos-latest}
           - {python: '3.12'}
-          - {name: Windows, python: '3.12', os: windows-latest}
-          - {name: Mac, python: '3.12', os: macos-latest}
           - {python: '3.11'}
           - {python: '3.10'}
           - {name: PyPy, python: 'pypy-3.11', tox: pypy311}