Fix transaction metrics tests failing

In commit 6ca7e976 (transactions: Scale registered metric by registered voters, 2020-07-14), we changed the "registered" metric for transactons to be scaled by the voter count. Due to a semantic merge conflict, this now causes tests to fail that have been added in afba66a3 (transactions: Expose info about voting outcomes, 2020-07-06).

Let's fix this by correctly scaling metrics as expected in transaction tests.