Resolve "Strike through the whole line when vulnerability is dismissed"

What does this MR do?

Adds CSS to strikethrough the entire line

1. there are buttons and text under .is-dismissed
2. the margin left never gets striked so I created the whitespace through ::after pseudo-class

Screenshots (if relevant)

before	after

Does this MR meet the acceptance criteria?

• Conform by the code review guidelines
  • Has been reviewed by a Frontend maintainer
• EE specific content should be in the top level /ee folder
• Conform by the merge request performance guides
• Conform by the style guides

What are the relevant issue numbers?

Closes #6005 (closed)