examples scatter_simulation.py fails with STIR 6.0

[KrisThielemans]

https://github.com/SyneRBI/SIRF/blob/master/examples/parameter_files/scatter_template.hs does not contain Maximum number of non-arc-corrected bins :=, leading to a default value of 0. This now raises an error due to UCL/STIR#1402, even though the value is set later (as far as I can remember).

Easiest is to add

 Maximum number of non-arc-corrected bins := 63

We can then just as well fix

SIRF/examples/Python/PET/scatter_simulation.py

Lines 11 to 12 in 36ed16d

	-p <path>, --path=<path> path to data files, defaults to data/examples/PET
	subfolder of SIRF root folder

the default is

SIRF/examples/Python/PET/scatter_simulation.py

Line 55 in 36ed16d

data_path = os.path.join(os.path.dirname(__file__), '..', '..', 'parameter_files')

Are we not running these examples in Github Actions?