Quarantine a flaky test (#20003)

src/Servers/Kestrel/test/FunctionalTests/MaxRequestBufferSizeTests.cs

@@ -203,6 +203,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.FunctionalTests
         }
 
         [Fact]
+        [QuarantinedTest]
         public async Task ServerShutsDownGracefullyWhenMaxRequestBufferSizeExceeded()
         {
             // Parameters