ci: Enable GL 4.3 tests on GL hosts via vtest

Since in the GL CTS each set set for a certain version inherits
all the tests for older versions, we can actually drop all previous
versiond and run only the GL 4.3 set.

Signed-off-by: Gert Wollny <gert.wollny@collabora.co.uk>
Part-of: <https://gitlab.freedesktop.org/virgl/virglrenderer/-/merge_requests/1167>
3 files changed