PUSH_TEST_IMAGES not passed into `./build.sh`

When a job is manually triggered via https://gitlab.developers.cam.ac.uk/uis/devops/infra/dockerimages/-/pipelines/new and PUSH_TEST_IMAGES=True and FORCE_DYNAMIC_JOBS=True, PUSH_TEST_IMAGES is not passed into ./build.sh and thus images are never pushed to the container registry.