Add CtsNNAPITestCases to mainline test mapping for neuralnetwork.

Bug: 185970126
Test: unittest
      forrest
Change-Id: I320f509e32cd2760065ea9fd6d9d31934767a601
diff --git a/TEST_MAPPING b/TEST_MAPPING
index 8973eb1..a8e0fdc 100644
--- a/TEST_MAPPING
+++ b/TEST_MAPPING
@@ -1,4 +1,9 @@
 {
+  "mainline-presubmit": [
+    {
+      "name": "CtsNNAPITestCases[com.google.android.neuralnetworks.apex]"
+    }
+  ],
   "presubmit": [
     {
       "name": "NeuralNetworksTest_utils"