`constrained-generators`: Improve haddocks #18923

Job	Run time
gen-hie	6m 11s
cabal-format	6s
fourmolu	44s
Check branch history	11s
build (9.12.2, ubuntu-latest)	6m 15s
build (9.8.4, ubuntu-latest)	5m 37s
build (9.10.2, ubuntu-latest)	4m 1s
shellcheck	6s
build (9.6.7, ubuntu-latest)	5m 46s
Check if formal-ledger-specifications SRP is valid	13s
${{ matrix.package }}-${{ matrix.ghc }}-${{ matrix.os }}	1s
codegen	1s
Tests completed	2s
Send a slack notification on \#ledger-internal if the nightly build failed	1s
	29m 15s

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