[quant][test] Add mul_scalar test (#46106)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46106
make sure quantized::mul_scalar matches dequantize - mul - quantize
Test Plan: Imported from OSS
Reviewed By: dskhudia
Differential Revision: D24230790
fbshipit-source-id: 1adcc82b9c41f1b53c9a761477f7c5c08aba1001
