when converting scripted model to coremltools, Unknown type bool encountered in graph lowering. This type is not supported in ONNX export.

## 🐛 Bug

getting this error
`Unknown type bool encountered in graph lowering. This type is not supported in ONNX export.`

## To Reproduce

Steps to reproduce the behavior:

1. run this colab https://colab.research.google.com/drive/13tF8p9x4FCPG0KEC_PBEEMianWKo8mfG?usp=sharing

which basically grabs a visual transformer from time, and tries to convert to torchscript to coreml

## Expected behavior

should not get the error

## Environment

colab

Start by running the linked Colab reproduction for the visual-transformer TorchScript-to-Core ML conversion and capture where the bool type reaches graph lowering. Read the graph-lowering and ONNX-export path implicated by the error; done means the reproduction converts without the unsupported-bool error.

Written by the indexing model from the issue text.