[3.15] gh-151126: Fix PyErr_NoMemory errors in _ctypes.c (GH-152720) (GH-153710)

gh-151126: Fix `PyErr_NoMemory`  errors in `_ctypes.c`  (GH-152720)
(cherry picked from commit d807210)

Co-authored-by: stevens <lipengyu@kylinos.cn>

Author: miss-islington

Misc/NEWS.d/next/Library/2026-07-01-11-29-13.gh-issue-151126.eElGy5.rst

@@ -0,0 +1,3 @@
+Fix a crash caused by failing to set :exc:`MemoryError` on allocation failure
+when passing :class:`ctypes.Structure` or :class:`ctypes.Union` instances by
+value to ctypes foreign functions.

Modules/_ctypes/_ctypes.c

@@ -673,6 +673,7 @@ StructUnionType_paramfunc(ctypes_state *st, CDataObject *self)
     if ((size_t)self->b_size > sizeof(void*)) {
         ptr = PyMem_Malloc(self->b_size);
         if (ptr == NULL) {
+            PyErr_NoMemory();
             return NULL;
         }
         memcpy(ptr, self->b_ptr, self->b_size);