Fix a potential race condition in the test decorators for enabling/disabling native funcol (#120833)
Previous, we parametrize some tests to run with both native and py funcol by flipping a global variable. However, some of these tests are multi-threaded tests, and the parametrization mechanism could lead to race condition.
This PR changes the mechansim to use `mock.patch` which is applied on a per-thread basis.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/120833
Approved by: https://github.com/wconstab
