material-package uuid validation is not correct

[donmahallem]

Currently the validate_json_schema.py script more or less doesn't work as intended for material-packages

OpenPrintTag Arch states:

Brand of the package is considered to be same as the brand of the material (Material::brand)

and doesn't have a brand attribute which is checked against here:

openprinttag-database/scripts/validate_json_schema.py

Lines 336 to 339 in 8ddbe73

	# Extract brand slug from format: brand: { slug: "value" }
	brand_ref = package_data.get('brand')
	if not brand_ref or not isinstance(brand_ref, dict):
	continue