Basic headless render test for Eevee and Cycles CPU. Did this because I
got a bit tired of testing render manually for both renderers (though
it’s not that much work).
Note that `render.threads` config is used only by Cycles. Using 1 thread
chosen because it’s not meaningfully slower than more for this render,
and it simplifies things to just pick 1 instead of making it dynamic.
Have chosen 32 samples since it’s not meaningfully slower than 1 (even
with `--cores 1`), and it’s not so small that maybe it’s not
representative, and too-low a number and there are artifacts that may
make it appear like something is broken.
Cycles denoising needs openimagedenoise and is not currently included in
aarch64 build.
0c101e7a04