Ignore duplicate attempts at questions when counting.

[rtibbles]

Summary

• Duplicate attempts at a question in a quiz can sometimes occur
• This can then result in a confusing user experience
• We already account for this in the backend when doing summarization and aggregation, but not in the learner UI
• This fixes that by doing a count of attempts made unique by item

References

Fixes #8922

Reviewer guidance

This bug is hard to reproduce, so I'd suggest doing an inspection of the code and ensuring this introduces no regressions.

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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
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• 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

[sairina]

lgtm - the map seems to have the correct number of questions that were attempted.