Including the kernel image in test-base requires rebuilding every
x86_64 container image on each kernel uprev, even though only the
crosvm jobs use this kernel.
Move the download to runtime and update the distribution tags to avoid
triggering container rebuilds on kernel changes.
Signed-off-by: Valentine Burley <valentine.burley@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34813>