Migrate GUI colors test to original CSS color format

Author: GuillaumeGomez

tests/rustdoc-gui/stab-badge.goml

@@ -26,16 +26,16 @@ define-function: (
 
 call-function: ("check-badge", {
     "theme": "ayu",
-    "color": "rgb(197, 197, 197)",
-    "background": "rgb(49, 69, 89)",
+    "color": "#c5c5c5",
+    "background": "#314559",
 })
 call-function: ("check-badge", {
     "theme": "dark",
-    "color": "rgb(221, 221, 221)",
-    "background": "rgb(49, 69, 89)",
+    "color": "#ddd",
+    "background": "#314559",
 })
 call-function: ("check-badge", {
     "theme": "light",
-    "color": "rgb(0, 0, 0)",
-    "background": "rgb(255, 245, 214)",
+    "color": "black",
+    "background": "#fff5d6",
 })