gh-159739: Release tuple items if resizing fails (GH-159754)

Release the references still held by the original tuple when
reallocation fails.

Backport to 3.15 and 3.14.

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

Author: jelle-openai

Misc/NEWS.d/next/C_API/2026-10-19-19-33-35.gh-issue-159739.dee9a0.rst

@@ -0,0 +1 @@
+Fix a reference leak when :c:func:`_PyTuple_Resize` fails.

Objects/tupleobject.c

@@ -1066,6 +1066,11 @@ _PyTuple_Resize(PyObject **pv, Py_ssize_t newsize)
 #ifdef Py_REF_DEBUG
         _Py_DecRefTotal(_PyThreadState_GET());
 #endif
+        /* The failed reallocation leaves the original items owned by v. */
+        i = oldsize;
+        while (--i >= 0) {
+            Py_XDECREF(v->ob_item[i]);
+        }
         PyObject_GC_Del(v);
         return -1;
     }