Update learn-quizzes.json to fix vague explanation (issue #13247)

[nayasinghania]

Description

I added "This is not the only correct answer." to the explanation as to why the other answer choices are wrong and "all of the above" is the correct answer.

Related Issue

https://github.com/ethereum/ethereum-org-website/issues/13247

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[wackerow]

Hey @raspberri05! Any reason we closed this out? Looks good to me for the issue it's solving.

[nayasinghania]

Sorry, was a mistake. Ive reopened it here #13380