Fix url generation for KaTeX fonts

What does this MR do?

Fixes #214722 (closed) in which it was identified that urls for KaTeX fonts were being incorrectly generated as url([object Module]) instead of something like url(/assets/webpack/KaTeX_AMS-Regular.cd28a1d7.woff2). This caused visual errors in rendered math blocks.

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Does this MR meet the acceptance criteria?

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