Accepting potential consequences is not the same as oneself cutting things off. Germany did not seek to end supplies then and there.

Edit: there was never any chance of Germany invading Ukraine then/joining Russia on any invasion.

It doesn't matter what they wanted to do. What matters is what happened. As a result of their actions they got cut off. If Germany had invaded Ukraine (via Poland?) the gas might still be on. Of course we don't know that because other countries would likely take offense to that action and I'm not willing to predict how the world would change if they had. (I can't even imagine change would cause them to be willing to invade in the first place, much less how everyone else would respond.)

Politics often are about the unintended consequences. Often they are also unforeseen.