Fix: Add unokai theme to builtins list

[karamanliev]

Description

This PR adds the unokai builtin vim theme to the builtins list. Currently, if you open the colorscheme picker with ignore_builtins = true set, the unokai option is still present.

unokai was introduced in to vim with this commit.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

It's a miniature change - you open the colorscheme picker and the unokai theme is not present anymore :)

Configuration:

• Neovim version (nvim --version): v0.11.0
• Operating system and version: Linux 6.14.3-arch1-1

Checklist:

• My code follows the style guidelines of this project (stylua)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (lua annotations)