r300/ci: add basic nine testing

Build Xnine tests in the gl testing container and enable them on r300.

The Xnine tests are mostly a selected wined3d tests imported to Xnine https://github.com/axeldavy/Xnine Xnine itself is a library to allow to run d3d9 apps on linux without Wine. The test coverage is not very extensive, but at least for r300 having this minimal coverage would have helped me to catch all the r300 nine regressions in the last few years that I'm aware of, so this is something I really want to have.