Herwig 7.3 release note. - Bewick, Gavin; Ferrario Ravasio, Silvia; Gieseke, Stefan; Kiebacher, Stefan; Masouminia, Mohammad R.; Papaefstathiou, Andreas; Plätzer, Simon; Richardson, Peter; Samitz, Daniel; Seymour, Michael H.; Siódmok, Andrzej; Whitehead, James (European Physical Journal C -- Particles & Fields, 2024)