Bulk email: fix messages && selector
Bulk email: fix messages && selector

Messages (alerts) were not training-agnostic (they were intended for
trainees). Trainees were replaced with "people".

Selector for one tag was not ended with `]`.

swcarpentry/amy,pbanaszkiewicz/amy,pbanaszkiewicz/amy,vahtras/amy,vahtras/amy,swcarpentry/amy,swcarpentry/amy,vahtras/amy,pbanaszkiewicz/amy