ci: bring back some i915 testing

Anholt's farm seems to be down long-term and while I don't have that much interest in i915 per se, it would help to have some i915 testing from time to time when I'm working on random core changes/fixes relevant for old HW. Additionally there seems to be some recent fixes for i915 from @noblock and @GKraats which are having troubles getting review. Maybe having a CI to independently verify at least the piglit and dEQP impact would help.

This runner is old DELL optiplex machine I got for free from @dh for r300 farm.

CC @anholt