Add improve contrast for Monokai theme suggest highlight

What does this MR do and why?

When typing a keyword that is suggested in the pipeline editor with autocomplete, it becomes blue and impossible to see.

This issue only happens for the white and none themes for the editor.

Closes #343659 (closed)

Screenshots or screen recordings

How to set up and validate locally

1. Open a project with .gitlab-ci.yml file in the WebIDE
   • If using GDK: /Commit451/lab-coat/-/blob/master/.gitlab-ci.yml
2. Delete the line "stage" and when you type it again it should appear.

During development I could only see the autocomplete working for WebIDE.

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.