skip_infer for SkipGroupNorm in SymbolicShapeInference (microsoft#18630)

### Description
<!-- Describe your changes. -->
microsoft#18273 added
`SkipGroupNorm` contrib op but it did not skip onnx shape inference for
this op in `SymbolicShapeInference`.

This leads to failed shape inference of the transformers optimized model
with `enable_skip_group_norm=True`. Also results in an invalid float16
model for the SD CUDA example.

This PR adds `SkipGroupNorm` to `skip_infer` so that it skips onnx shape
inference for this op and instead uses the relevant dispatcher.


### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
Fix shape inference failure for models with `SkipGroupNorm` nodes.

onnxruntime/python/tools/symbolic_shape_infer.py

@@ -467,6 +467,7 @@ def _onnx_infer_single_node(self, node):
             "PythonOp",
             "MultiHeadAttention",
             "GroupNorm",
+            "SkipGroupNorm",
             "BiasSplitGelu",
             "BiasAdd",
             "NhwcConv",