Build release binaries on post-submit (#406)
Build release binaries on post-submit (#406)

Release binaries include the Debian packages for Ubuntu 18.04 and 20.04
and static linux binaries for x86_64.

The binaries are built from main and the release branches whenever a
new commit is pushed there, and the artifacts are automatically attached
to releases in GitHub when a release is created.
libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl