Update taxonomies/packaging_materials.txt
Update taxonomies/packaging_materials.txt

added PLA acronym(en)

Co-authored-by: Stéphane Gigandet <36bd4f73be32ed7262c164e7ee72163e7543989e@openfoodfacts.org>
openfoodfacts/openfoodfacts-server,openfoodfacts/openfoodfacts-server,openfoodfacts/openfoodfacts-server,openfoodfacts/openfoodfacts-server,openfoodfacts/openfoodfacts-server