Add TEST_MAPPING for GtsUnofficialApisUsageTestCases

Bug: 123701384
Test: m and watch if treehugger triggers the test
Change-Id: Ib1793c778e97e130e33049e962752fbe4c684222
diff --git a/api/TEST_MAPPING b/api/TEST_MAPPING
index 8a676e9..2cdf54b 100644
--- a/api/TEST_MAPPING
+++ b/api/TEST_MAPPING
@@ -2,6 +2,9 @@
   "presubmit": [
     {
       "name": "CtsCurrentApiSignatureTestCases"
+    },
+    {
+      "name": "GtsUnofficialApisUsageTestCases"
     }
   ]
 }