CardsLayoutGallery: do not use deprecated hiddenActions list

Remove usage of deprecated hiddenActions list and use the displayHint property instead.

src/data/contents/ui/gallery/CardsLayoutGallery.qml

@@ -20,7 +20,7 @@
 import QtQuick 2.6
 import QtQuick.Controls 2.0 as Controls
 import QtQuick.Layouts 1.2
-import org.kde.kirigami 2.4 as Kirigami
+import org.kde.kirigami 2.20 as Kirigami
 
 import "components"
 
@@ -137,12 +137,11 @@ Kirigami.ScrollablePage {
                     Kirigami.Action {
                         text: qsTr("Action2")
                         icon.name: "address-book-new-symbolic"
-                    }
-                ]
-                hiddenActions: [
+                    },
                     Kirigami.Action {
                         text: qsTr("Action always hidden")
                         icon.name: "add-placemark"
+                        displayHint: Kirigami.DisplayHint.AlwaysHide
                     }
                 ]
                 banner {