Correct, agapanthus or Lily of the Nile. The tubers are supposedly toxic. We do have a post by one member whose sulcata ate a mess of tulip tubers and got a nasty face rash, I’d keep my tortoise far away from them.
I guess you could try offering a leaf in the enclosure, they aren’t harmful. Or you could avoid them entirely, in an abundance of caution,
Again, back to some basic generalities. Things that grow from tubers or bulbs are usually best to avoid. Grasses, dandelions, plantain and a host of other good plants, trees & bushes are out there, no sense taking risks on other “questionable” plants.