Allow quiz level learners see fixed order to be edited after a quiz is opened.

[rtibbles]

Summary

• The API previously disallowed editing the quiz level learner_sees_fixed_order attribute for section randomization - but as it has no effect on the recording of data and the review of the answers for the coach, this is safe.
• The UI also allowed this, which resulted in unexpected 400s.
• This PR updates the API to allow this so the UI and the API are in step.

References

Fixes #12289

Reviewer guidance

Create a quiz.
Start the quiz.
Edit the quiz.
Update the Section Order property.
Save - see that it saves without errors, and that when returning to the edit page after refreshing, it is properly updated to the new value.

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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-.pex
Windows Installer (EXE)	kolibri-0.17.0a0.dev0+git.33.g864811a6-windows-setup-unsigned.exe
Debian Package	kolibri_0.17.0a0.dev0+git.33.g864811a6-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.17.0a0.dev0+git.33.g864811a6-0.4.2.dmg
Android Package (APK)	kolibri-0.17.0a0.dev0+git.33.g864811a6-0.1.3-debug.apk
TAR file	kolibri-0.17.0a0.dev0+git.33.g864811a6.tar.gz
WHL file	kolibri-0.17.0a0.dev0+git.33.g864811a6-py2.py3-none-any.whl

[nucleogenesis]

Gave the code a look and things LGTM - are you planning to add anything here? If not then should be good to go when QA gets a look at it.

[rtibbles]

No, this is complete, just needs QA.

[pcenov]

LGTM!