Motivation:
When a build fails, it's desirable to have the build artifacts available
so the build failure can be inspected, investigated and hopefully fixed.
Modification:
Change the Makefile and CI workflow such that the build artifacts are
captured and uploaded when the build fails.
Result:
A "target.zip" file is now available for download on failed GitHub
Actions builds.
Also schedule a build to run at 06:30 in the morning, every Monday.
This way, the JDK and Netty 5 snapshots will be updated in the build cache every week.
