reduce number of parallel people tasks

MediaBrowser.Server.Implementations/Library/LibraryManager.cs

@@ -690,7 +690,7 @@ namespace MediaBrowser.Server.Implementations.Library
         /// <returns>Task.</returns>
         public async Task ValidatePeople(CancellationToken cancellationToken, IProgress<double> progress)
         {
-            const int maxTasks = 250;
+            const int maxTasks = 50;
 
             var tasks = new List<Task>();