fix indexer in Autoassess supermeans module use a tuple of (slice(), idx, idx)

[valeriupredoi]

Description

Found while running diags for release in #2833 - the indexer was a list like list[slice(), idx, idx] which is deprecated, and now fully retired behaviour, but a tuple of that is well liked by Numpy. Can I gets a quick a-ok here plese much? 🍺

Closes #2837

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[sloosvel]

Recipes finish successfully with this change, but maybe someone more familiar with the results should check if they are consistent

[valeriupredoi]

cheers muchly @sloosvel - not a worry, this module (the supermeans one) will be retired soon, plus, the tuple of slice, index, index is identical to what was previously a list of the same elements, so the output array is identical. Gonna merge 🍺