Updates design tokens used in buttons to match the darkmode
design direction.

feat(GlButton): Update design tokens for darkmode

See merge request !4705



Merged-by: Vanessa Otto <votto@gitlab.com>
Approved-by: Dan MH <dmizzi-harris@gitlab.com>
Approved-by: Vanessa Otto <votto@gitlab.com>
Reviewed-by: Sascha Eggenberger <seggenberger@gitlab.com>
Co-authored-by: Sascha Eggenberger <seggenberger@gitlab.com>

# [98.1.0](v98.0.0...v98.1.0) (2024-10-21)

### Features

* **GlButton:** Update design tokens for darkmode ([61852296](61852296))