fix canvas problem file import

[abeglova]

What are the relevant tickets?

https://github.com/mitodl/hq/issues/8877

Description (What does it do?)

This pr fixes a bug that causes the pdf to markdown job for canvas problem files to be run unnecessarily when the files have not changed

It also prevents tika from being run for files whose content is set by the pdf to markdown job.

How can this be tested?

From the shell run

from learning_resources.tasks import sync_canvas_courses
sync_canvas_courses(['14566'], False)

you might see some messages from LiteLLM:
LiteLLM completion() model= gpt-4o; provider = openai

Run

sync_canvas_courses(['14566'], False)

again. You should not see more messages from LiteLLM