do not throw when unicode is seen in pull request info (#18195)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18195
ghimport-source-id: 05102cb115c6bd6d141f51905e20155bcd79a908
Stack from [ghstack](https://github.com/ezyang/ghstack):
* **#18195 [build] do not throw when unicode is seen in pull request info**
Differential Revision: D14529707
fbshipit-source-id: 2f6a31b01b3a9b044fd24be466cc5325b70929ad
