Update _icon.html.erb

[ItsJulian]

Description

The invalid icon was not showing when a PR was marked as invalid

Requirements to merge

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code in hard-to-understand areas
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes

[ItsJulian]

This PR fixes issue #575

[MattIPv4]

576