ci/virgl: Fix GLES31 testing on desktop GL.
The version overrides leaked into the virglrenderer server, breaking compiling of all sorts of shaders. We already get GLES3.1 when running virgl on llvmpipe GL without doing any overrides.
The version overrides leaked into the virglrenderer server, breaking compiling of all sorts of shaders. We already get GLES3.1 when running virgl on llvmpipe GL without doing any overrides.