games/vkquake: update to 1.20.3

Changes: https://github.com/Novum/vkQuake/releases/tag/1.13.0
Changes: https://github.com/Novum/vkQuake/releases/tag/1.13.1
Changes: https://github.com/Novum/vkQuake/releases/tag/1.20.0
Changes: https://github.com/Novum/vkQuake/releases/tag/1.20.1
Changes: https://github.com/Novum/vkQuake/releases/tag/1.20.2
Changes: https://github.com/Novum/vkQuake/releases/tag/1.20.3