Add Python 3.15 and free-threaded to the CI

Author: filmor

.github/workflows/ci.yml

@@ -74,7 +74,7 @@ jobs:
             instance: macos-15
             suffix:   -macos-aarch64-none
 
-        python: ['3.14', '3.13', '3.12', '3.11', '3.10']
+        python: ['3.15', '3.15t', '3.14t', '3.14', '3.13', '3.12', '3.11', '3.10']
 
         exclude:
           # Fails to call mono methods