fix bug : Volume test iOS sound

wasn't working anymore, seems since iOS 14, see https://stackoverflow.com/questions/69023854/ios-15-notification-sounds-are-not-playing-for-foreground-notifications and https://developer.apple.com/forums/thread/700884 ("Displaying" sound only notifications is no longer possible.)

The solution is
- to add a dummy text and body in the test notification
- to add .list if iOS 14 or higher

xdrip/View Controllers/Root View Controller/RootViewController.swift

@@ -2982,7 +2982,12 @@ extension RootViewController: UNUserNotificationCenterDelegate {
         }  else if notification.request.identifier == ConstantsNotifications.notificationIdentifierForVolumeTest {
             
             // user is testing iOS Sound volume in the settings. Only the sound should be played, the alert itself will not be shown
-            completionHandler([.sound])
+            if #available(iOS 14.0, *) {
+                completionHandler([.sound, .list])
+            } else {
+                // Fallback on earlier versions
+                completionHandler([.sound])
+            }
             
         } else if notification.request.identifier == ConstantsNotifications.notificationIdentifierForxCGMTransmitterDelegatexDripError {
             

xdrip/View Controllers/SettingsNavigationController/SettingsViewController/SettingsViewModels/SettingsViewAlertSettingsViewModel.swift

@@ -71,9 +71,9 @@ struct SettingsViewAlertSettingsViewModel:SettingsViewModelProtocol {
             
             // define and set the content
             let content = UNMutableNotificationContent()
-            // body and title will not be shown, so contents can be empty
-            content.body = ""
-            content.title = ""
+            // body and title will not be shown, because app is in the foreground
+            content.body = "will not be shown"
+            content.title = "will not be shown"
             // sound
             content.sound = UNNotificationSound.init(named: UNNotificationSoundName.init("xdripalert.aif"))
             // notification request