Add cos_patch_trailer_check in PRESUBMIT.cfg.

cos_patch_trailer_check will check whether cos-patch
trailer is present or not. In case it is not present,
`repo upload` will fail.

BUG=b/173034990
TEST=manual test on changelist.
RELEASE_NOTE=None

Change-Id: I3e671300858315f0d94c5de72c84b3d9a187938e
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/8682
Reviewed-by: Dexter Rivera <riverade@google.com>
Tested-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
diff --git a/PRESUBMIT.cfg b/PRESUBMIT.cfg
index 6e0e040..e66280f 100644
--- a/PRESUBMIT.cfg
+++ b/PRESUBMIT.cfg
@@ -8,3 +8,6 @@
 
 # Make sure RELEASE_NOTE field is present.
 release_note_field_check: true
+
+# Make sure cos_patch trailer is present.
+cos_patch_trailer_check: true