`constrained-generators`: Improve haddocks #18992

Job	Run time
shellcheck	6s
build (9.8.4, ubuntu-latest)	1m 33s
build (9.6.7, ubuntu-latest)	1m 33s
gen-hie	1m 32s
build (9.12.2, ubuntu-latest)	1m 31s
build (9.10.2, ubuntu-latest)	1m 25s
fourmolu	42s
Check branch history	11s
cabal-format	9s
Check if formal-ledger-specifications SRP is valid	14s
codegen	1s
${{ matrix.package }}-${{ matrix.ghc }}-${{ matrix.os }}	1s
Tests completed	4s
Send a slack notification on \#ledger-internal if the nightly build failed	1s
	9m 3s

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