Acceptance Tests: bump Avocado version requirement to 85.0 This is being proposed as a separate single patch simply to show that no known regressions have been introduced as far as the acceptance tests/jobs are related. CI job: https://gitlab.com/cleber.gnu/qemu/-/pipelines/255122420 This version (and 84.0) contain improvements that address specific QEMU use cases, including: * Being able to download and use Fedora 31 images and thus re-activate the "boot_linux.py" tests * Being able to register local assets via "avocado assets register" and use them in tests