Depends on the airline, Qantas and a few others require it now irrespective of the destinations requirements
Qantas claims on its website that the PCR test is an Australian government requirement, not QF's. I wonder if they haven't updated the travel *to* Australia requirements to reflect that we can now travel *from* Australia?
If what QF says is true, all carriers would require the same PCR test before boarding.
*edited to add* the latest 'flying update' email from QF says you only need to be vaccinated, no mention of the PCR test.