`constrained-generators`: Improve haddocks #18939

Job	Run time
Check branch history	10s
cabal-format	8s
fourmolu	49s
gen-hie	7m 30s
build (9.8.4, ubuntu-latest)	7m 51s
Check if formal-ledger-specifications SRP is valid	15s
build (9.10.2, ubuntu-latest)	7m 53s
build (9.12.2, ubuntu-latest)	7m 51s
build (9.6.7, ubuntu-latest)	7m 51s
shellcheck	5s
${{ matrix.package }}-${{ matrix.ghc }}-${{ matrix.os }}	1s
codegen	1s
Tests completed	4s
Send a slack notification on \#ledger-internal if the nightly build failed	1s
	40m 30s

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