That probably depends on the requirements for a Biology Masters in a particular program. You may need some other chemistry courses which are not part of the requirements for an astronomy major or bio minor, and perhaps stats, if it isn’t already a required course.
But, as I wrote - check the prerequisites for entering a biology master’s program. Look at a few programs that you would target when applying for your masters.
You should also definitely reach out to a number of astrobiologists and ask them about their path, and, in general, start networking - it is never too soon to start networking.