Update ci.yml

Author: vboutrou

.github/workflows/ci.yml

@@ -47,6 +47,7 @@ jobs:
         uses: matlab-actions/run-command@v2
         with:
           command: openProject(pwd); RunAllTests; 
+          startup-options: -nodisplay
 
       # Upload the test results as artifact
       - name: Upload TestResults