Migrate GUI colors test to original CSS color format

Author: GuillaumeGomez

tests/rustdoc-gui/docblock-table.goml

@@ -36,17 +36,17 @@ define-function: (
 )
 
 call-function: ("check-colors", {
-    "theme": "dark",
-    "border_color": "rgb(224, 224, 224)",
-    "zebra_stripe_color": "rgb(42, 42, 42)",
+    "theme": "ayu",
+    "border_color": "#5c6773",
+    "zebra_stripe_color": "#191f26",
 })
 call-function: ("check-colors", {
-    "theme": "ayu",
-    "border_color": "rgb(92, 103, 115)",
-    "zebra_stripe_color": "rgb(25, 31, 38)",
+    "theme": "dark",
+    "border_color": "#e0e0e0",
+    "zebra_stripe_color": "#2a2a2a",
 })
 call-function: ("check-colors", {
     "theme": "light",
-    "border_color": "rgb(224, 224, 224)",
-    "zebra_stripe_color": "rgb(245, 245, 245)",
+    "border_color": "#e0e0e0",
+    "zebra_stripe_color": "#f5f5f5",
 })