PR #3384 introduced code that resets sys.last_traceback and friends by assigning None to them:

The normal CPython behaviour here is that once the exception has been cleared, the attributes are deleted rather than set to None. Could I suggest updating this line of code to delete the attributes?

For context: the Nones caused test failures in another project when we attempted to switch from unittest discover to pytest as our test runner; we had a test for some complex code that was messing with various sys attributes including the sys.last_* attributes, and the test verified that those attributes were unchanged by the code under test.