in `set_reweighted_injections` change `NumberOfEvents` to `NumberOfInjections` for clarity

in set_reweighted_injections change NumberOfEvents to NumberOfInjections for clarity https://git.ligo.org/zoheyr-doctor/popsummary/-/blob/v0.0.1_review/popsummary/popresult.py?ref_type=heads#L242