Correctly create empty ints for Constant in rewriter (#2497)

Due to changes onnx/ir-py#148, we cannot create
an empty list attribute without specifying type because it would be
ambiguous.

Fix #2496

Signed-off-by: Justin Chu <justinchuby@users.noreply.github.com>

Author: justinchuby

onnxscript/rewriter/ort_fusions/shape_optimization.py

@@ -55,7 +55,7 @@ def rewrite(self, op, dim0, dim1, dim2, dim3, **_):
         transposed_dims = [dim0, dim2, dim1, dim3]
         sliced_result = transposed_dims[self._start_val : self._end_val]
         if len(sliced_result) == 0:
-            return op.Constant(value_ints=[])
+            return op.Constant(value_ints=ir.AttrInt64s("value_ints", []))
         if len(sliced_result) == 1:
             return op.Identity(sliced_result[0])
         return op.Concat(*sliced_result, axis=0)