Suppress message `Joining with `by = join_by(Level)`

[MichaelGuggisberg-meraki]

When calling plot on class multisynth.summary it outputs a message Joining with by = join_by(Level).

This should be able to be fixed by changing line 913 of multisynth_class.R to summ$att %>% inner_join(last_times, by = "Level") %>%