The mirrored reads counters get incremented for any mirrored read, general or targeted. Not explicitly setting samping to 0 on general mirrored reads leaves the on at a default value, so there's a small chance any request is sampled for a general mirrored read. Such a request may be delayed, and arrive after testing the baseline for a targeted mirrored reads test, thus making counters show an additional mirrored read. This seems to have caused [BF-44836](https://jira.mongodb.org/browse/BF-44836), and this PR is to fix that race.