Adding empty coverage-file

So that combining and storing as artifact does not fail

.gitlab-ci.yml

@@ -66,6 +66,7 @@ test_JUWELS:
     # - touch benchmarks/output.json
     - echo $SYSTEMNAME
     - sbatch --wait etc/juwels_${SHELL_SCRIPT}.sh
+    - touch .coverage.empty
     - python -m coverage combine
     - mv .coverage coverage_${SHELL_SCRIPT}.dat
   after_script: