Modify tests to use assertWarnsOnceRegex instead of maybeWarnsRegex (#52387)
Summary:
Related to https://github.com/pytorch/pytorch/issues/50006
Follow on for https://github.com/pytorch/pytorch/issues/48560 to ensure TORCH_WARN_ONCE warnings are caught. Most of this is straight-forward find-and-replace, but I did find one place where the TORCH_WARN_ONCE warning was not wrapped into a python warning.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/52387
Reviewed By: albanD
Differential Revision: D26773387
Pulled By: mruberry
fbshipit-source-id: 5be7efbc8ab4a32ec8437c9c45f3b6c3c328f5dd
