Merge branch 'gray-900_v2' into 'master'

Update $gray-900 to match gitlab-ui palette

Closes #228727

See merge request gitlab-org/gitlab!36778

app/assets/stylesheets/framework/variables.scss

@@ -171,7 +171,7 @@ $gray-500: #a7a7a7 !default;
 $gray-600: #919191 !default;
 $gray-700: #707070 !default;
 $gray-800: #4f4f4f !default;
-$gray-900: #2e2e2e !default;
+$gray-900: #303030 !default;
 $gray-950: #1f1f1f !default;
 
 $greens: (