Fix compiler warning on Windows

..\Modules\_testcapimodule.c(3320): warning C4098: 'matmulType_dealloc' : 'void' function returning a value
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index 291eee6..750e90f 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -3317,7 +3317,7 @@
 static void
 matmulType_dealloc(PyObject *self)
 {
-    return Py_TYPE(self)->tp_free(self);
+    Py_TYPE(self)->tp_free(self);
 }
 
 static PyNumberMethods matmulType_as_number = {