Build testng with core_current

Using core_current ensures that the module is not using any Android APIs
(e.g. APIs under android.* packages), but only core Java APIs.

Bug: 72206056
Test: m -j testng
Change-Id: I30528e49267c88af6f02d2b82891a1599e6f7663
diff --git a/Android.bp b/Android.bp
index cd41f54..25ba36a 100644
--- a/Android.bp
+++ b/Android.bp
@@ -43,6 +43,7 @@
     name: "testng",
     host_supported: true,
     hostdex: true,
+    sdk_version: "core_current",
 
     srcs: [
         "src/main/**/*.java",