Fix vulnerability save button spinner position

What does this MR do?

When viewing the vulnerability details for a vulnerability on the security dashboard:

The user can add a comment to a history item at the bottom. Clicking on the "Add a comment" text will show a textarea that lets the user input a comment:

Clicking on the Save button shows a spinner while the comment is being saved. However, the spinner is positioned incorrectly. This MR fixes that.

Before	After

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