test_linalg: triangular_solve - make well_conditioned well conditioned (#105919)
`well_contioned=True` does not guarantee that the samples for `triangular_solve` are actually well-conditioned. This PR fixes that. This issues was discovered in https://github.com/pytorch/pytorch/pull/104425.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/105919
Approved by: https://github.com/lezcano
