Update scoring code to ignore test targets

[priyakasimbeg]

Given the update in the rules to exclude test targets from scoring we should update scoring.py.
Specifically get_index_that_reaches_target should ignore the test target when it gets the index.

[priyakasimbeg]

To be more specific, these lines need to be updated: https://github.com/mlcommons/algorithmic-efficiency/blob/main/scoring/scoring.py#L130-L139