Render markup in on-demand scans errors

What does this MR do?

Ensures that links are correctly rendered in on-demand DAST scans alerts.

How to test this?

1. As a Developer, navigate to a project's on-demand scans form at /:namespace/:project/-/on_demand_scans/new.
2. Fill-out the form and click on Save and run scan.
   • You should see an alert containing a link above the form.
3. Navigate back to the DAST profiles library at /:namespace/:project/-/security/configuration/dast_scans.
4. Try running a scan from the Saved scans tab.
   • You should see an alert containing a link at the top of the list.

Screenshots (strongly suggested)

Page	Before	After
On-demand scans form
DAST profiles library

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• [-] Documentation (if required)
• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Related to #326356 (closed)