How to regulate 29VAC down to 24VAC?
For a "power supply" that consists of a merely stepdown transformer, and with only a light load attached, that's pretty normal (16% high).

When a load is attached (when it is driving the solenoids) the voltage will drop a bit. Even if it was actually 16% high under load, it should not be a problem for the solenoids unless the ambient temperature is extremely high- close to the maximum for the solenoids. It will cause about 1/3 more heating, so if the coils heated to 50°C at room temperature they would heat to closer to 58°C.