add whispering fungi as a possible spawn in group_fungi_zombie

[zdlpoppa]

Summary

Features "Adds whispering fungi to fungi zombie mongroup."

Purpose of change

Incredibly quick PR, this monster is also meant to spawn in this mongroup, but wasn't added.

Describe the solution

Include it in the mongroup, simple 1 line addition

Describe alternatives you've considered

N/A

Testing

added, and it spawns

Additional context

Oops