Move the tests to postsubmit group

The tests are failing on ToT.

Bug: 123852953
Test: None
Change-Id: I2e75c99d913f6954290aa9d6aada8797bf931977
diff --git a/fs_mgr/libfs_avb/TEST_MAPPING b/fs_mgr/libfs_avb/TEST_MAPPING
index dc23827..b0f36d4 100644
--- a/fs_mgr/libfs_avb/TEST_MAPPING
+++ b/fs_mgr/libfs_avb/TEST_MAPPING
@@ -1,5 +1,5 @@
 {
-  "presubmit": [
+  "postsubmit": [
     {
       "name": "libfs_avb_test",
       "host": true