Make asyncTaskTest backward compatible

Test:  atest CtsOsTestCases
Bug: 160006699

Change-Id: Ice2dd839a1d43dfd0768e36d0e06f663325f77f9
diff --git a/tests/tests/os/Android.bp b/tests/tests/os/Android.bp
index e04630b..1fcb10a 100644
--- a/tests/tests/os/Android.bp
+++ b/tests/tests/os/Android.bp
@@ -59,4 +59,5 @@
     ],
     // Do not compress minijail policy files.
     aaptflags: ["-0 .policy"],
+    min_sdk_version : "29"
 }