Disable OpenAIAssistant structured output integration tests (#4451)

Skip all three structured output run tests in
OpenAIAssistantStructuredOutputRunTests as they fail intermittently
on the build agent/CI, matching the pattern already used in
AzureAIAgentsPersistentStructuredOutputRunTests.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: SergeyMenshykh

dotnet/tests/OpenAIAssistant.IntegrationTests/OpenAIAssistantStructuredOutputRunTests.cs

@@ -1,9 +1,23 @@
 // Copyright (c) Microsoft. All rights reserved.
 
+using System.Threading.Tasks;
 using AgentConformance.IntegrationTests;
 
 namespace OpenAIAssistant.IntegrationTests;
 
 public class OpenAIAssistantStructuredOutputRunTests() : StructuredOutputRunTests<OpenAIAssistantFixture>(() => new())
 {
+    private const string SkipReason = "Fails intermittently on the build agent/CI";
+
+    [Fact(Skip = SkipReason)]
+    public override Task RunWithResponseFormatReturnsExpectedResultAsync() =>
+        base.RunWithResponseFormatReturnsExpectedResultAsync();
+
+    [Fact(Skip = SkipReason)]
+    public override Task RunWithGenericTypeReturnsExpectedResultAsync() =>
+        base.RunWithGenericTypeReturnsExpectedResultAsync();
+
+    [Fact(Skip = SkipReason)]
+    public override Task RunWithPrimitiveTypeReturnsExpectedResultAsync() =>
+        base.RunWithPrimitiveTypeReturnsExpectedResultAsync();
 }