ci: Improve binary build jobs

ci: Improve binary build jobs

For x86_64, build in an Alma Linux 8 container since RHEL 8 is the
oldest still active LTS mainstream Linux distribution to my knowledge.

For aarch64, cross compile in an x86_64 environment instead of in a
native aarch64 environment. This is because I want to be able to build
release binaries locally on my x86_64 machine if there is some problem
with the CI environment and it feels good to match that in CI. The build
is still on Ubuntu 22.04 – I made a quick attempt to get
cross-compilation working in Alma Linux 8 working but gave up.