[3.11] gh-101656: Fix "conversion from Py_ssize_t to int" warning in _testcapimodule (#101680)

(cherry picked from commit acc2f3b19d)

Modules/_testcapimodule.c

@@ -6179,11 +6179,11 @@ eval_eval_code_ex(PyObject *mod, PyObject *pos_args)
         globals,
         locals,
         c_args,
-        c_args_len,
+        (int)c_args_len,
         c_kwargs,
-        c_kwargs_len,
+        (int)c_kwargs_len,
         c_defaults,
-        c_defaults_len,
+        (int)c_defaults_len,
         kw_defaults,
         closure
     );