LibWeb: Implement css gradient-interpolation-method

Author: https://github.com/Gingeh
Commit: 31853c13d3
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3638
Reviewed-by: https://github.com/AtkinsSJ ✅
Reviewed-by: https://github.com/LucasChollet

Libraries/LibWeb/HTML/HTMLHRElement.cpp

@@ -68,7 +68,7 @@ void HTMLHRElement::apply_presentational_hints(GC::Ref<CSS::CascadedProperties>
         // the user agent is expected to treat the attribute as a presentational hint setting the element's 'color' property to the resulting color.
         if (name == HTML::AttributeNames::color) {
             if (auto parsed_value = parse_legacy_color_value(value); parsed_value.has_value()) {
-                cascaded_properties->set_property_from_presentational_hint(CSS::PropertyID::Color, CSS::CSSColorValue::create_from_color(*parsed_value));
+                cascaded_properties->set_property_from_presentational_hint(CSS::PropertyID::Color, CSS::CSSColorValue::create_from_color(*parsed_value, CSS::ColorSyntax::Legacy));
             }
         }
         // https://html.spec.whatwg.org/multipage/rendering.html#the-hr-element-2:maps-to-the-dimension-property