Fix Python 3.15 Windows CI

Tests fails on Windows with Python 3.15:
"unresolved external symbol PyInit_test_pythoncapi_compat_cext_c11".

Author: vstinner

tests/setup.py

@@ -12,10 +12,12 @@
 # Set to true to debug C/C++ extensions in gdb
 DEBUG = False
 
+MS_WINDOWS = (sys.platform == 'win32')
 FREE_THREADING = bool(sysconfig.get_config_var('Py_GIL_DISABLED'))
 if sys.implementation.name == 'cpython':
     if FREE_THREADING:
-        TEST_LIMITED_C_API = (sys.version_info >= (3, 15))
+        # FIXME: test the limited C API on Windows
+        TEST_LIMITED_C_API = (sys.version_info >= (3, 15)) and not MS_WINDOWS
     else:
         TEST_LIMITED_C_API = True
 else:

tests/test_pythoncapi_compat_cext.c

@@ -2654,7 +2654,7 @@ module_exec(PyObject *module)
 
 
 // On Python 3.15 and newer, use PySlot API
-#if PY_VERSION_HEX >= 0x030F0000
+#if PY_VERSION_HEX >= 0x030F0000 && !defined(MS_WINDOWS)
 
 PyABIInfo_VAR(abi_info);