Remove extra empty space from MR page

What does this MR do?

remove some margin-bottom from the issue container on MR page. Instead add margin to the actual flash-error elements (so only add margin when there is actually an error)

Screenshots (strongly suggested)

before	after

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines