libsnapshot: Disable another legacy merge path in tests.

Bug: 279009697
Test: presubmit
Change-Id: I1954b38f497bb8e4f7aa288e80541ac9ad5c075c
diff --git a/fs_mgr/libsnapshot/snapshot_test.cpp b/fs_mgr/libsnapshot/snapshot_test.cpp
index f472bab..1fbfaf7 100644
--- a/fs_mgr/libsnapshot/snapshot_test.cpp
+++ b/fs_mgr/libsnapshot/snapshot_test.cpp
@@ -2646,6 +2646,11 @@
     ASSERT_TRUE(init->InitiateMerge());
     ASSERT_EQ(UpdateState::MergeFailed, init->ProcessUpdateState());
 
+    if (ShouldSkipLegacyMerging()) {
+        LOG(INFO) << "Skipping legacy merge in test";
+        return;
+    }
+
     // Simulate a reboot that tries the merge again, with the non-failing dm.
     ASSERT_TRUE(UnmapAll());
     init = NewManagerForFirstStageMount("_b");