Israel doesn’t have any problems with Russia helping Assad fight the terrorists who are trying to bring down his regime.
But there is no way that these missiles would be any use whatever against the terrorist threat. Their only possible use is against Israel.
Basically, that’s also why Israel attacked Syria recently—because Assad was threatening to arm the Palestinians who want to kill Israelis.
Actually, it is more likely given the tensions between Turkey and Syria that the missiles are more intended as a way to deter Turkey from attacking Syria, which is far more of a possibility than Israel getting involved.