Fix tests

Author: ufechner7

.github/workflows/CI.yml

@@ -38,4 +38,6 @@ jobs:
           arch: ${{ matrix.arch }}
       - uses: julia-actions/cache@v2
       - uses: julia-actions/julia-buildpkg@v1
-      - uses: julia-actions/julia-runtest@v1
+      - run: sudo apt-get update && sudo apt-get install -y xorg-dev mesa-utils xvfb libgl1 freeglut3-dev libxrandr-dev libxinerama-dev libxcursor-dev libxi-dev libxext-dev
+      - run: DISPLAY=:0 xvfb-run -s '-screen 0 1024x768x24' julia --project -e 'using Pkg; Pkg.instantiate()'
+      - run: DISPLAY=:0 xvfb-run -s '-screen 0 1024x768x24' julia --project --code-coverage=user -e "using TestEnv; TestEnv.activate(); include(\"test/runtests.jl\")"