Fix cddl for `update_committee` cold credenteial #16834

Job	Run time
fourmolu	45s
gen-hie	5m 35s
build (8.10.7, ubuntu-latest)	49m 4s
cabal-format	8s
build (9.2.8, ubuntu-latest)	33m 8s
build (9.6.6, ubuntu-latest)	28m 5s
Check branch history	12s
Check if formal-ledger-specifications SRP is valid	13s
build (9.8.4, ubuntu-latest)	21m 50s
build (9.10.1, ubuntu-latest)	21m 16s
${{ matrix.package }}-${{ matrix.ghc }}-${{ matrix.os }}	1s
Send a slack notification on \#ledger-internal if the nightly build failed	1s
Tests completed	1s
	2h 40m 19s

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