Change HB alerts to raise

[justinlittman]

• https://github.com/sul-dlss/was_robot_suite/blob/main/lib/robots/dor_repo/was_crawl_preassembly/start.rb#L13
• https://github.com/sul-dlss/was_robot_suite/blob/main/lib/robots/dor_repo/was_seed_preassembly/start.rb#L13