Workaround .net error serializing new object()

See https://github.com/dotnet/runtime/issues/61995

src/Readarr.Api.V1/ProviderControllerBase.cs

@@ -102,9 +102,10 @@ namespace Readarr.Api.V1
         }
 
         [RestDeleteById]
-        public void DeleteProvider(int id)
+        public object DeleteProvider(int id)
         {
             _providerFactory.Delete(id);
+            return new { };
         }
 
         [HttpGet("schema")]