If anyone thinks Github boycotting ICE will change anything of ICE's conduct, that to me is some kind of Delusions of Grandeur. The money involved are a tiny part of a forgotten section of their budget. If they don't think it will change anything, we can agree that this boycott is purely symbolic and will accomplish nothing.
As for “only being symbolic”, no, it wouldn’t. It would allow workers to be in an environment where their work supports their values. A lot of these workers are going to leave the org to go work for a company that doesn’t so conflict with their values, as is absolutely their prerogative in a free labor market. This is actually a mature way to let GitHub understand the full costs of their actions, so that they can make an informed decision. There’s literally no problem here, this is a functioning labor dynamic.