Add and test events in `pallet-conviction-voting` #14304

Job	Run time
preflight / preflight	31s
preflight / ci-versions	1m 14s
check-runtime-migration (westend)	7m 55s
check-runtime-migration (asset-hub-westend)	5m 24s
check-runtime-migration (bridge-hub-westend)	4m 46s
check-runtime-migration (collectives-westend)	4m 51s
check-runtime-migration (coretime-westend)	5m 7s
All runtime migrations passed	1s
	29m 49s

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