Fix instance norm input size validation + test (#56659)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/45687
Fix changes the input size check for `InstanceNorm*d` to be more restrictive and correctly reject sizes with only a single spatial element, regardless of batch size, to avoid infinite variance.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56659
Reviewed By: pbelevich
Differential Revision: D27948060
Pulled By: jbschlosser
fbshipit-source-id: 21cfea391a609c0774568b89fd241efea72516bb
