When shutting down, the main worker context closes. This causes the
subprocess to be killed, which in turn caused a task execution error. This
now no longer happens, as such errors are expected on shutdown and do not
indicate task failure.
The add-on code was copy-pasted from other addons and used the GPL v2
license, whereas by accident the LICENSE text file had the GNU "Affero" GPL
license v3 (instead of regular GPL v3).
This is now all streamlined, and all code is licensed as "GPL v3 or later".
Furthermore, the code comments just show a SPDX License Identifier
instead of an entire license block.
