Fix typo explitic

[philderbeast]

A follow on from #11501. This changes a couple of data constructors in Cabal.

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[geekosaur]

It has (finally) occurred to me to wonder if we can define bidirectional pattern synonyms with the old names for constructors like this, and mark them as deprecated so users get warnings. We might then remove them in 3.20. I won't block the PR on that, though.