Add clean workspace step to clang-tidy workflow (#71655)
Summary:
Should alleviate instances of "blah not a repository" that happen due to non-ephemeral runners not cleaning up properly.
https://github.com/pytorch/pytorch/runs/4902228068?check_suite_focus=true
Pull Request resolved: https://github.com/pytorch/pytorch/pull/71655
Reviewed By: malfet
Differential Revision: D33719058
Pulled By: janeyx99
fbshipit-source-id: 4ff35893d00c99026154d71e4d1ae7a54ac5c42a
(cherry picked from commit 13ca9d1f91b9101a6350d3caf45fbc158e7ae47a)
