[ONNX] Support conv-bn fusion in blocks (#66152) (#67272)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/67272
* Support conv-bn fusion in nested blocks
* avoid running script tests twice
Test Plan: Imported from OSS
Reviewed By: msaroufim
Differential Revision: D31962513
Pulled By: malfet
fbshipit-source-id: 3ee79426542f9049cf62ac7b0c1be9d60ae6d014
