Add monkey_test to input postsubmit

It needs to run for a bit in postsubmit before we can add it to
presubmit.

Bug: 328347986
Test: (cd frameworks/native/services/inputflinger && atest)
Change-Id: I69c622d2c766896e222bc0f2a8df441cf8496132
diff --git a/services/inputflinger/TEST_MAPPING b/services/inputflinger/TEST_MAPPING
index fe4d0cd..5ab4e71 100644
--- a/services/inputflinger/TEST_MAPPING
+++ b/services/inputflinger/TEST_MAPPING
@@ -284,6 +284,9 @@
     },
     {
       "name": "CtsInputHostTestCases"
+    },
+    {
+      "name": "monkey_test"
     }
   ],
   "staged-platinum-postsubmit": [