Issue #18408: Fix call_exc_trace(): if the traceback is NULL, use None when
building the tuple (type, value, traceback) passed to the callback.

PyTuple_Pack() does crash if an argument is NULL.
#18399: fix comment typo.

Patch by Andrew Rowe.
Merge: #18399: fix comment typo.
#18424: PEP8ify the tense of the sum docstring.
Merge: #18424: PEP8ify the tense of the sum docstring.
#18116: getpass no longer always falls back to stdin.

Also fixes a resource warning that occurred when the fallback is taken.

Patch by Serhiy Storchaka.

(We couldn't figure out how to write tests for this.)