Disable btri tests on Windows if MAGMA is not found (#17989)
Summary:
Fixes #17988
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17989
Reviewed By: ezyang
Differential Revision: D14454571
Pulled By: soumith
fbshipit-source-id: fc39a807a597d3574f4ca4e22cea12194e4693c0
