Follow-up from "Draft: test: fix dal covalidity test"

The Incremental.begin_operation prepare the alpha_context for the application of the next block. Here the problem as that we want the alpha context of the previous block, specially because we depends on the level.

The fix would be to adds rpc or similar so we don't have to call the Incremental.begin_operation for this test.

The following discussion from !7755 (merged) should be addressed:

• @Saroupille started a discussion: (+4 comments)

  It is not enough to remove this succ?