`constrained-generators`: Improve haddocks #18981

Job	Run time
shellcheck	8s
build (9.6.7, ubuntu-latest)	18m 25s
fourmolu	47s
build (9.8.4, ubuntu-latest)	16m 49s
build (9.12.2, ubuntu-latest)	16m 13s
cabal-format	6s
Check branch history	12s
Check if formal-ledger-specifications SRP is valid	14s
gen-hie	7m 14s
build (9.10.2, ubuntu-latest)	15m 12s
Tests completed	6s
Send a slack notification on \#ledger-internal if the nightly build failed	0s
codegen	0s
${{ matrix.package }}-${{ matrix.ghc }}-${{ matrix.os }}	0s
	1h 15m 26s

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