fix: 修两个小问题

Author: Starrah

chart/mai/MaiChart.cs

@@ -41,7 +41,7 @@ public override decimal StartBpm {
         }
     }
     public override decimal StartTime => (decimal)FirstNoteTime.Seconds;
-    public override decimal EndTime => (decimal)ToSecond(Notes.Select(x=>x.EndTime).Max());
+    public override decimal EndTime => (decimal)ToSecond(Notes.Max(x=>x.EndTime));
     public override int TotalNotes => Statistics.Total;
 
     /**

chart/mai/Note.cs

@@ -28,7 +28,7 @@ public virtual int Key
         get => _key;
         set
         {
-            if (value < 1 || value > 8) throw new ArgumentException(string.Format(Locale.InvalidKey, value));
+            if (value is < 1 or > 8) throw new ArgumentException(string.Format(Locale.InvalidKey, value));
             _key = value;
         }
     }