Migrate GUI colors test to original CSS color format

Author: GuillaumeGomez

Diff for: tests/rustdoc-gui/run-on-hover.goml

@@ -33,22 +33,22 @@ define-function: (
 
 call-function: ("check-run-button", {
     "theme": "ayu",
-    "color": "rgb(120, 135, 151)",
+    "color": "#788797",
     "background": "rgba(57, 175, 215, 0.09)",
-    "hover_color": "rgb(197, 197, 197)",
+    "hover_color": "#c5c5c5",
     "hover_background": "rgba(57, 175, 215, 0.37)",
 })
 call-function: ("check-run-button", {
     "theme": "dark",
-    "color": "rgb(222, 222, 222)",
+    "color": "#dedede",
     "background": "rgba(78, 139, 202, 0.2)",
-    "hover_color": "rgb(222, 222, 222)",
+    "hover_color": "#dedede",
     "hover_background": "rgb(78, 139, 202)",
 })
 call-function: ("check-run-button", {
     "theme": "light",
-    "color": "rgb(245, 245, 245)",
+    "color": "#f5f5f5",
     "background": "rgba(78, 139, 202, 0.2)",
-    "hover_color": "rgb(245, 245, 245)",
+    "hover_color": "#f5f5f5",
     "hover_background": "rgb(78, 139, 202)",
 })