pythongh-115142: Skip test__xxsubinterpreters if _testinternalcapi is not available (python#116507)

Author: Eclips4

Lib/test/test__xxsubinterpreters.py

@@ -7,14 +7,14 @@
 import threading
 import unittest
 
-import _testinternalcapi
 from test import support
 from test.support import import_helper
 from test.support import os_helper
 from test.support import script_helper
 
 
 interpreters = import_helper.import_module('_xxsubinterpreters')
+_testinternalcapi = import_helper.import_module('_testinternalcapi')
 from _xxsubinterpreters import InterpreterNotFoundError