Don't fail when a lesson or exam is assigned through multiple ways.

[rtibbles]

Summary

• Fixes bug where an exam or lesson assigned via a class and a group (for example) would cause an error during the post sync hooks because of multiple objects being returned

References

Unreported bug, but could have been the cause of syncing errors.

Reviewer guidance

This just takes the first assignment, any issues with this?

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Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.16.0b13.dev0_git.12.g622152b7.pex
Windows Installer (EXE)	kolibri-0.16.0b13.dev0+git.12.g622152b7-unsigned.exe
Debian Package	kolibri_0.16.0b13.dev0+git.12.g622152b7-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.16.0b13.dev0+git.12.g622152b7-0.3.0.dmg
Android Package (APK)	kolibri-0.16.0b13.dev0+git.12.g622152b7-0.1.0-debug.apk
TAR file	kolibri-0.16.0b13.dev0+git.12.g622152b7.tar.gz
WHL file	kolibri-0.16.0b13.dev0+git.12.g622152b7-py2.py3-none-any.whl

[rtibbles]

Sorry, @rtibbles, we decided to go in a different direction.