AO3-5870 Make blockquote borders not overlap with user icons in comments

[slavalamp]

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• Have you added tests for any changed functionality?
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Issue

https://otwarchive.atlassian.net/browse/AO3-5870

Purpose

Makes it so blockquotes at the beginning of a comment always have their borders visible (making it clear they're blockquotes) and not behind the commenter's icon

Credit

slavalamp

[sarken]

Thanks!