Remove not selector increasing specificity of rules

What does this MR do?

When this was added - https://gitlab.com/gitlab-org/gitlab-ce/commit/b352462d01e3c51d09314c282e84afe075d6ad01#4b8ec5ff8ab825db349011c80b5bc9f401b2085d_753_752 - it increased the specificity of the rule, overriding all the other CSS.

Added the li tag to the rule we need, in order to increase that rule specificity.

Fix isn't great, it just increases the snow ball of specificity in our selectors, but can't find a better one without a refactor :(

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Review
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/38958