The build calls to Protonmail's repo and builds from it. When that repo changes (i.e. when deb/* changes), the image should be built again.
Currently, that repo changed a few days ago, and the "build" image has not updated in a year. I don't see a reason to never update the image when the upstream repo updates frequently.
* Adjust GitHub CI to also build for riscv64
* Update base Ubuntu base for build from 18.04 LTS to 20.04 LTS as to support riscv64
* Minor: Exclude idea IDE files from git