We're now getting errors on CI due to gcc-13 being missing. We can
probably be smarter about what packages we install, depending on the
workflow being run. But let's first unblock CI.
The error we get is a bit strange and inconsistent. Some CI runners seem
to already have gcc-13 installed. Others don't and can't find the gcc-13
package without the test Ubuntu toolchain PPA.
Unfortunately a composite action cannot have a `post:` step like
JavaScript actions are allowed to have, so we need to explicitly call
the post/save actions ourselves from the workflow file when we want to
save Toolchain/QEMU/ccache caches.
Co-Authored-By: Timothy Flynn <trflynn89@pm.me>
