Fix tutorial's g.region use for GRASS 8

[petrasovaa]

Running through the tutorial I noticed a problem here:
https://itzi.readthedocs.io/en/latest/tutorial.html#adjust-the-region

g.region behavior changed little bit in GRASS 8. Now when you specify save parameter, it assumes you don't want to change the current region as well, so in this case you would either need to use new -o flag:

g.region -po raster=elev_lid792_1m@PERMANENT res=5 save=lidar_5m

or don't save the region (I don't see it used anywhere, but I may be wrong):

g.region -p raster=elev_lid792_1m@PERMANENT res=5

The current state results in the simulation being run at 1 m, so it takes a long time.