With QEMU the ARM64 builds are slow and not reliable. If we use the
Docker Cloud builders we reduce the build times considerably.
As a Docker OSS organisation we get 400 build minutes per month, which
should be fine, because we already use checks if builds are really
needed. The Docker Cloud also uses a cache that should reduce build
times a little bit more.
The old version of "build-branches.sh" skipped the pushing of images when one of
them didn't change its sources. When looking at the Netbox branches I noticed
that the "master" branch only changes when there is a new release. Because we
build the new releases anyway in "build-latest.sh" that leaves "develop" and
"develop-*" which change regularly. The new script "build-next.sh" is responsible
for building "develop-*" as the next major release of Netbox. The build of
"develop" is moved to the Github Action build matrix. This has the additional
advantage of being faster because more builds are done in parallel.
