performance_schema.replication_group_member_stats table has the
column 'COUNT_TRANSACTIONS_VALIDATING', which indicates the number
of transactions rows present in the certification info, that one
can execute certification with them, but they haven't been Garbage
Collected yet. The column name 'COUNT_TRANSACTIONS_VALIDATING' is
not proportionable with its meaning.

To fix the problem, the column COUNT_TRANSACTIONS_VALIDATING is
renamed to COUNT_TRANSACTIONS_ROWS_VALIDATING.