Follow hlint suggestion: use lambda-case

[philderbeast]

See #9110. Discharges and no longer ignores HLint's "use lambda-case" suggestion so that these will be suggested by our CI linting.

I'll squash commits before applying the merge label if this pull request is approved. I've left the styling change to module CmdHaddockProject separate for an easier review.

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• Patches conform to the coding conventions.
• Is this a PR that fixes CI? If so, it will need to be backported to older cabal release branches (ask maintainers for directions).

[jappeace]

nice!

[ulysses4ever]

I'm borderline on lambda case: I like to use it myself a lot but I'd rather we don't force it on contributors: arguably, this raises the bar a bit, and I've seen Haskell newcomers who were deeply confused by this syntax.

But since the necessary two approvals are in and my doubts aren't backed by any real data, I won't block it.