Change notification dot color to red

What does this MR do and why?

closes https://jihulab.com/gitlab-cn/gitlab/-/issues/1515

Screenshots or screen recordings

before	after

How to set up and validate locally

set env GITLAB_SIMULATE_SAAS=1 and browse the page on GDK

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.