Fix `station_data.csv` values for 20120529_M5.6_EmiliaRomagna

Reported in the user's forum:
https://groups.google.com/g/openquake-users/c/7HxAsiF47cQ

> Comparing the values provided in the csv file with those from the ITACA website from INGV (https://itaca.mi.ingv.it/ItacaNet_32/#/event/IT-2012-0011), it appears that the PGA_VALUE is that in the Z-direction.

