also run PR tests in virtual x environment (allowing UI tests)

.github/workflows/pullrequest.yml

@@ -23,4 +23,4 @@ jobs:
           java-version: ${{ env.JAVA_VERSION }}
           cache: 'maven'
       - name: Build and Test
-        run: mvn -B clean install jacoco:report -Pcoverage,dependency-check
+        run: xvfb-run mvn -B clean install jacoco:report -Pcoverage,dependency-check