another problem:

there're two tests under delta-merge-test still using other engine than DeltaMerge.

https://github.com/pingcap/tics/blob/452ffe6edfcb5b8a74d9087f548f24b0910c4fc3/tests/delta-merge-test/query/expr/json.test#L5

https://github.com/pingcap/tics/blob/452ffe6edfcb5b8a74d9087f548f24b0910c4fc3/tests/delta-merge-test/query/expr/logical_op.test#L5

we should modify them for adapting DeltaMerge if there's no strong reason.