Fix a security warning (microsoft#18979)

Description (reference:
GHSA-5crp-9r3c-p9vr)
Newtonsoft.Json prior to version 13.0.1 is vulnerable to Insecure
Defaults due to improper handling of expressions with high nesting level
that lead to StackOverFlow exception or high CPU and RAM usage.
Exploiting this vulnerability results in Denial Of Service (DoS).

To mitigate the issue one either need to update Newtonsoft.Json to
13.0.1 or set MaxDepth parameter in the JsonSerializerSettings.
```
JsonConvert.DefaultSettings = () => new JsonSerializerSettings { MaxDepth = 128 };
```
This file is the only place using `JsonConvert`, so I blindly put this
fix and hope the warning will disappear.

Author: wschin

csharp/test/Microsoft.ML.OnnxRuntime.EndToEndTests.Mobile/EndToEndTests.Mobile.Automation/Tests.cs

@@ -40,10 +40,12 @@ public void RunPlatformUnitTest()
             var serializedResultSummary = _app.Invoke(_getResultsBackdoorMethodName)?.ToString();
             Assert.IsNotEmpty(serializedResultSummary, "Test results were not returned");
 
+            // Fix security issue (overflow with too much nesting): GHSA-5crp-9r3c-p9vr
+            JsonConvert.DefaultSettings = () => new JsonSerializerSettings { MaxDepth = 128 };
             var testSummary = JsonConvert.DeserializeObject<TestResultSummary>(serializedResultSummary);
             Assert.AreEqual(testSummary.Failed, 0, $"{testSummary.Failed} tests failed");
 
             _app.Screenshot("Post-testing");
         }
     }
-}
+}

csharp/test/Microsoft.ML.OnnxRuntime.Tests.Devices/TestResultProcessor.cs

@@ -45,8 +45,9 @@ public TestResultSummary GetResults()
         public string GetSerializedResults()
         {
             var resultSummary = GetResults();
+	    JsonConvert.DefaultSettings = () => new JsonSerializerSettings { MaxDepth = 128 };
             var serializedResultSummary = JsonConvert.SerializeObject(resultSummary, Formatting.Indented);
             return serializedResultSummary;
         }
     }
-}
+}