feat: add os field in appcast item

Author: LucasXu0

packages/auto_updater/lib/src/appcast.dart

@@ -40,6 +40,7 @@ class AppcastItem {
     this.maximumOperatingSystemVersionIsOK,
     this.channel,
     this.criticalUpdate,
+    this.os,
   });
 
   factory AppcastItem.fromJson(Map<String, dynamic> json) =>
@@ -62,6 +63,7 @@ class AppcastItem {
   final bool? maximumOperatingSystemVersionIsOK;
   final String? channel;
   final bool? criticalUpdate;
+  final String? os;
 
   Map<String, dynamic> toJson() => _$AppcastItemToJson(this);
 }

packages/auto_updater/lib/src/appcast.g.dart

@@ -35,6 +35,7 @@ extension SUAppcastItem {
             "maximumOperatingSystemVersionIsOK": self.maximumOperatingSystemVersionIsOK,
             "channel": self.channel ?? "",
             "criticalUpdate": self.isCriticalUpdate,
+            "os": self.osString,
         ]
         return dict;
     }