fix: xblock-poll's celery tasks were not registered (#28019)

[pomegranited]

Pulled from https://github.com/edx/edx-platform/pull/28019

(cherry picked from commit e2a867e)

Testing instructions

Sandbox provisioning:

• LMS: https://pr391.sandbox.stage.opencraft.hosting/
• Studio: https://studio.pr391.sandbox.stage.opencraft.hosting/

1. Login to the LMS as a learner. (Note: stage sandboxes use self-signed certificates, so you'll need to accept that risk to view the https content.)
2. Navigate to the poll and survey blocks added to the Demo course under Example Week 3 Be Social > More ways to connect.
3. Ensure you can generate and download the CSV reports.

Reviewer

• @eLRuLL

[eLRuLL]

@pomegranited ty for including this, I checked the sandbox instance and it's working great, approved 👍