Rollup merge of #111844 - GuillaumeGomez:migrate-gui-test-color-4, r=notriddle

Migrate GUI colors test to original CSS color format

I updated the `browser-ui-test` version because I fixed GuillaumeGomez/browser-UI-test#507. If inside a function, the colors were not considered, preventing the second commit of this PR.

Follow-up of rust-lang/rust#111459.

r? `@notriddle`

Author: Dylan-DPC