You're in Europe. Your house has a "Whole house RCD". It detects current flow between places electricity should go, and places electricity should not. (aka "residual current" or a "ground fault".
The RCD is tripping because a small amount of current is leaking from the heating element (presumably through the tinfoil) to the chassis of the oven. The oven's safety earthing is doing its job. The heating element is not; it should be insulated by ceramic material, which I gather has spalled off over the years.
So, in the short term, you can fix this by removing the rest of the aluminum foil. However, that heating element desperately needs to be replaced. Having tinfoil touch it should not matter. In the meantime, the RCD will continue to protect the oven from starting a fire. As far as protecting you from getting shocked, not quite as much; that RCD trips on 30 milliamps, and that's enough to stun and rarely kill. Human-rated RCDs trip at 6 milliamps.