[FormRecognizer] Enable StartBuildModelSucceedsWithValidPrefix (Azure#27708)

Author: kinelski

sdk/formrecognizer/Azure.AI.FormRecognizer/tests/DocumentModelAdministrationClient/DocumentModelAdministrationClientLiveTests.cs

@@ -113,14 +113,13 @@ public async Task StartBuildModelWithNeuralBuildMode()
         }
 
         [RecordedTest]
-        [Ignore("Issue https://github.com/Azure/azure-sdk-for-net-pr/issues/1442")]
         public async Task StartBuildModelSucceedsWithValidPrefix()
         {
             var client = CreateDocumentModelAdministrationClient();
             var trainingFilesUri = new Uri(TestEnvironment.BlobContainerSasUrl);
             var modelId = Recording.GenerateId();
 
-            BuildModelOperation operation = await client.StartBuildModelAsync(trainingFilesUri, DocumentBuildMode.Template, modelId, new BuildModelOptions() { Prefix = "subfolder" });
+            BuildModelOperation operation = await client.StartBuildModelAsync(trainingFilesUri, DocumentBuildMode.Template, modelId, new BuildModelOptions() { Prefix = "subfolder/" });
 
             await operation.WaitForCompletionAsync();