try to make gLMakie work on remote

Author: rveltz

.github/workflows/CI.yml

@@ -37,3 +37,5 @@ jobs:
       - uses: julia-actions/cache@v1
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
+        with:
+           prefix: xvfb-run -s '-screen 0 1024x768x24'