Fix `BIT` column in unique key bug #1233

Job	Run time
docker-tests (mysql:8.4.3)	10m 33s
docker-tests (percona/percona-server:8.0.41-32)	10m 32s
docker-tests (mysql:8.0.41)	10m 34s
docker-tests (mysql/mysql-server:5.7.41)	10m 33s
	42m 12s

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