Switch to v-safe-html for Markdown Fields

What does this MR do and why?

Resolves #241857 (closed)

• Replace v-html with v-safe-html in app/assets/javascripts/vue_shared/components/markdown/field.vue

Screenshots or screen recordings

No visual changes for user

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.