chore(banner): Mark GlBanner as design compiliant again

What does this MR do?

GlBanner was design compiliant but it was failing before we fixed our proper build pipeline. Now with fixes to build pipeline we could safely bring flag again

Relevant issue: #800 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines.
• [-] GitLab UI's contributing guidlines.
• [-] If it changes a Pajamas-compliant component's look & feel, the MR has been reviewed by a UX designer.
• [-] If it changes GitLab UI's documentation guidelines, the MR has been reviewed by a Technical Writer.
• [-] If the MR changes a component's API, integration MR(s) have been opened in the following projects to ensure that the @gitlab/ui package can be upgraded quickly after the changes are released:
  • [-] GitLab: mr_url
  • [-] Customers Portal: mr_url
  • [-] Status Page: mr_url
• [-] Added the ~"component:*" label(s) if applicable.