Fix warning in _testembed.c (GH-13533)

diff --git a/Programs/_testembed.c b/Programs/_testembed.c
index 21d3b44..de1c587 100644
--- a/Programs/_testembed.c
+++ b/Programs/_testembed.c
@@ -1231,15 +1231,13 @@
 
 static int test_audit_subinterpreter(void)
 {
-    PyThreadState *ts;
-
     Py_IgnoreEnvironmentFlag = 0;
     PySys_AddAuditHook(_audit_subinterpreter_hook, NULL);
     _testembed_Py_Initialize();
 
-    ts = Py_NewInterpreter();
-    ts = Py_NewInterpreter();
-    ts = Py_NewInterpreter();
+    Py_NewInterpreter();
+    Py_NewInterpreter();
+    Py_NewInterpreter();
 
     Py_Finalize();