Reverted disposal of multipart data form (#3197)

Reverted faulty disposal logic of multipart data forms

Co-authored-by: Alan Rynne <[email protected]>

Core/Core/Transports/ServerUtils/ServerAPI.cs

@@ -402,7 +402,7 @@ private async Task UploadObjectsImpl(string streamId, List<List<(string, string)
     using HttpRequestMessage message =
       new() { RequestUri = new Uri($"/objects/{streamId}", UriKind.Relative), Method = HttpMethod.Post };
 
-    using MultipartFormDataContent multipart = new();
+    MultipartFormDataContent multipart = new();
 
     int mpId = 0;
     foreach (List<(string, string)> mpData in multipartedObjects)