Disable flaky test_proper_exit test. (#18950)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18950
ghimport-source-id: 27bd575fd3c73a51ace1360aa020fa63a792a5d2
Differential Revision: D14802009
Pulled By: ezyang
fbshipit-source-id: 051e1d038892c2c6e8337357fa80771b8dc42680
