Additionally run releasetools_test with Python 3.

Bug: 131631303
Test: TreeHugger
Test: `atest releasetools_test`
Test: `atest releasetools_py3_test`
Change-Id: Ie00f48835aae41bc69ab8554b856a62aa3b497cc
diff --git a/tools/releasetools/TEST_MAPPING b/tools/releasetools/TEST_MAPPING
index 77cef07..0af0f04 100644
--- a/tools/releasetools/TEST_MAPPING
+++ b/tools/releasetools/TEST_MAPPING
@@ -3,6 +3,10 @@
     {
       "name": "releasetools_test",
       "host": true
+    },
+    {
+      "name": "releasetools_py3_test",
+      "host": true
     }
   ]
 }