Very minor fixes for import code [FC-0036]

[bradenmacdonald]

• The import code that accepts a file object should have type BinaryIO (any file-like object that produces bytes), not BytesIO (specifically an in-memory bytes object and not a file handle)
• As I experienced, if a TypeError occurred during import (e.g. because you forgot to open the CSV file as binary instead of as a string...) then the import task would become permanently stuck because TypeError exceptions were not caught.

No need for a version bump with this fix.

Private ref: can be considered part of FAL-3531.

[openedx-webhooks]

Thanks for the pull request, @bradenmacdonald! Please note that it may take us up to several weeks or months to complete a review and merge your PR.

Feel free to add as much of the following information to the ticket as you can:

• supporting documentation
• Open edX discussion forum threads
• timeline information ("this must be merged by XX date", and why that is)
• partner information ("this is a course on edx.org")
• any other information that can help Product understand the context for the PR

All technical communication about the code itself will be done via the GitHub pull request interface. As a reminder, our process documentation is here.

Please let us know once your PR is ready for our review and all tests are green.

[openedx-webhooks]

@bradenmacdonald 🎉 Your pull request was merged! Please take a moment to answer a two question survey so we can improve your experience in the future.