checkpatch_presubmit: Skip all merge commits Bug: 341570880 Test: Verified that checkpatch is skipped for merge commits. Test: Verified that checkpatch is not skipped for non-merge commits. Change-Id: Ibc21d8c63a376d423ddc4cb1a1972309c0fc07d4 Signed-off-by: Erik Staats <[email protected]>