Do you have to use a 20A surge rated diode, for something that -- failing any further information -- perhaps doesn't need any protection at all?
Why not a clamp diode from GND to node to VCC? Or a smaller ESD diode from GND?
Note that you can tolerate much higher peak-clamping voltages, by adding a series resistor between TVS and MCU pin. It is doubtful that a pushbutton needs any kind of speed, so the limiting value of this resistance is determined by the internal pullup (assuming you don't want, or can't afford, an external pullup) and total node leakage.
Note also that, manufacturers only rate leakage as it is convenient to do so; likely in this case, when they say 800uA, they do mean it (though the typical value, at 25°C, will probably be much less), but this suspicion can be valid at much lower currents, say 1uA to 0.1uA, below which it is increasingly expensive (slow) to make an accurate measurement of, so ratings in this range may be expected to be much better, they just don't want to take the time to be able to say by how much (small MOS gates being an excellent example).
Tim