Correct Jira issue import known limitations around text parsing

What does this MR do?

This MR corrects the known limitation section of the Jira issue importer to say that Jira text formatting is not converted to GFM #379104 (comment 1151004657).

Related issues

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
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  • Style Guide.
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• ~"frontend"
• ~"backend"
• ~"type::bug"
• ~"database"

These labels cause the MR to be added to code verification QA issues.

Reviewer's checklist

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If you aren't sure which tech writer to ask, use roulette or ask in the #docs Slack channel.

• If the content requires it, ensure the information is reviewed by a subject matter expert.
• Technical writer review items:
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  • Ensure a release milestone is set.
  • If relevant to this MR, ensure content topic type principles are in use, including:
    • The headings should be something you'd do a Google search for. Instead of Default behavior, say something like Default behavior when you close an issue.
    • The headings (other than the page title) should be active. Instead of Configuring GDK, say something like Configure GDK.
    • Any task steps should be written as a numbered list.
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• Review by assigned maintainer, who can always request/require the reviews above. Maintainer's review can occur before or after a technical writer review.