Use v-if instead of passing empty string for severity

What does this MR do?

There are two components that use <severity-badge> and pass an empty string if there is no severity string available. Instead, we should use v-if to conditionally render the <severity-badge> instead of passing an empty string. An empty string will cause <severity-badge> to render a blank template, because the severity string is actually a lookup key and needs to match with one of the expected severity levels.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] 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 #208407 (closed)