Are you sure about that?
If a citizen establishes residency in GA, registers by the deadline (which passed yesterday), and meets all other criteria, then I'm not aware of any provision of law that could deny them the right to vote.
But I'm not necessarily talking about moving into Georgia temporarily for the run-off and moving back out, I'm talking more broadly about getting liberals in CA, NY, and other solid blue states to move permanently to purple and red states.
This would help undo the geographical bias inherent in the Electoral College, Senate malapportionment, and rampant gerrymandering at the state level.