I recently booked the Majestic Princess sailing on March 1, 2024 and got the same message from Princess. I just checked the Australian government's website and this is what is says:
From this date, you do not need to provide proof of a negative COVID-19 test to meet Australia's travel requirements. Some countries, airlines and vessel operators may require a pre-departure test result at check-in before you can board your flight or ship. Check the entry requirements of the country you are travelling or transiting through, and your airline or vessel operator’s requirements.