[Bug] Change subgraph runner tests to not graft onto subgraph head

[lutter]

Some of the subgraph runner tests graft directly onto the subgraph head. PR #5135 made that very verboten, which would make those tests fail. For expediency, the PR just disables the check that we graft at least reorg_threshold blocks back for debug builds.

The right fix for this would be to change the subgraph runner tests to set a small reorg threshold and to graft only outside that reorg threshold so that the check can be enabled for debug builds, too.

[github-actions]

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