synthesize a traceback to get a normal exc_info from an exception

[cosmicexplorer]

Problem

main is currently broken on 3.12:

> nox -e test-3.12 -- -k test_tempdir_cleanup_ignore_errors
...
FAILED tests/unit/test_utils_temp_dir.py::test_tempdir_cleanup_ignore_errors - TypeError: 'PermissionError' object is not subscriptable

While it seems like #11394 may have been the direct trigger for the test failure, it appears the error was first introduced earlier in a hasty attempt to remove some DeprecationWarnings (25f4e6e). It turns out that while the documentation at https://docs.python.org/3.12/library/shutil.html#shutil.rmtree still uses the name "excinfo" for the third argument to onexc, onexc actually has a BaseException for the third argument instead of a sys.exc_info(), as per https://docs.python.org/3.12/whatsnew/3.12.html#shutil.

Solution

• Since we don't use the sys.exc_info() parts anywhere, just convert any sys.exc_info() to a BaseException in our callback wrapper, and switch to explicitly only handling BaseException in our error callbacks.