Move `update` callback one `while` loop out in `pack_all_loose`

[GeigerJ2]

Currently, this is done for every loose object:

disk-objectstore/disk_objectstore/container.py

Lines 1434 to 1438 in 5b44f09

	if callback:
	callback(
	'update',
	obj_dict['size'],
	)

Instead, if we move it one while loop out, it will be done for every pack, whichh is probably what we want.