There's hardly any military work that would involve using code from GitHub in Crimea. All the R&D is done in mainland Russia. This targets common people who use GitHub for their pet projects or just regular work.

In general, this thread demonstrates that here there's very little understanding about the mass psychology of Russians, and, really, any nation other than Americans. No one in Crimea is going to rebel against the Russian government because of the U.S. sanctions against them exclusively. A policy like this only validates the Russian government's narrative of the U.S. going after Russia as such. If the U.S. government wanted to seek allies in Crimeans, they could perhaps focus on sanctioning Moscovian oligarchs. Well, except they won't, because Russian oligarchs that lose leverage in the Kremlin later make for good dissidents to be used by the U.S. as an ideological tool against Russia. And the oligarchic system is keeping Russia from modernizing, which is also in the U.S. interest.