fix: remove duplicate include of pycore_lock.h in _struct.c

Author: ashm-dev

Modules/_struct.c

@@ -9,10 +9,10 @@
 
 #include "Python.h"
 #include "pycore_bytesobject.h"   // _PyBytesWriter
+#include "pycore_lock.h"          // _PyOnceFlag_CallOnce()
 #include "pycore_long.h"          // _PyLong_AsByteArray()
 #include "pycore_moduleobject.h"  // _PyModule_GetState()
 #include "pycore_weakref.h"       // FT_CLEAR_WEAKREFS()
-#include "pycore_lock.h"          // _PyOnceFlag_CallOnce()
 
 #include <stddef.h>               // offsetof()