Enable CSSRelativeColorSyntaxEnabled preference

https://bugs.webkit.org/show_bug.cgi?id=242918
rdar://97279447

Reviewed by Sam Weinig and Myles C. Maxfield.

* Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml:

Canonical link: https://commits.webkit.org/258519@main

Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml

@@ -1032,16 +1032,16 @@ CSSPaintingAPIEnabled:
 
 CSSRelativeColorSyntaxEnabled:
   type: bool
-  status: testable
+  status: stable
   humanReadableName: "CSS Relative Color Syntax"
   humanReadableDescription: "Enable support for CSS Relative Color Syntax defined in CSS Color 5"
   defaultValue:
     WebKitLegacy:
-      default: false
+      default: true
     WebKit:
-      default: false
+      default: true
     WebCore:
-      default: false
+      default: true
 
 CSSScrollAnchoringEnabled:
   type: bool