Append "macOS beta" to the version dialog on macOS

src/PicView.Avalonia/Views/AboutView.axaml.cs

@@ -1,3 +1,4 @@
+using System.Runtime.InteropServices;
 using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Media;
@@ -19,6 +20,10 @@ public partial class AboutView : UserControl
         Loaded += (_, _) =>
         {
             AppVersion.Text = VersionHelper.GetCurrentVersion();
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
+            {
+                AppVersion.Text +=" macOS beta";
+            }
 
             if (!Settings.Theme.Dark && !Settings.Theme.GlassTheme)
             {