Run UpdatableSystemFontTest in postsubmit.

Bug: 176939176
Test: atest --test-mapping frameworks/base/tests/UpdatableSystemFontTest:postsubmit
Change-Id: I3aeb54cf8af6c3fb235ba13acbc24eb360f5237a
diff --git a/tests/UpdatableSystemFontTest/TEST_MAPPING b/tests/UpdatableSystemFontTest/TEST_MAPPING
new file mode 100644
index 0000000..a5c4479
--- /dev/null
+++ b/tests/UpdatableSystemFontTest/TEST_MAPPING
@@ -0,0 +1,7 @@
+{
+  "postsubmit": [
+    {
+      "name": "UpdatableSystemFontTest"
+    }
+  ]
+}