fix: import+export management commands

[kdmccormick]

Backports #28219 into Maple.

Why backport this fix into Maple, when Nutmeg is about to be released?

• This fix was cut on 12/9 (just after the Maple cut) so the only reason it wasn't part of Maple was dumb luck.
• The library import/export management commands are entirely broken in Maple. Even though Maple is about to go out of support, we should avoid having obviously-broken features in recent releases if possible.
• In the openedx-test-course I'm building, I'm testing every PR against the repo by using the latest stable Tutor release import the course and library. Without this patch, that workflow is broken.

FYI:

• @alex2bender and @bradenmacdonald (original authors)
• @regisb (release manager)