Add test stage to gitlab_ci.yml

The test stage currently just runs `ninja test`.

.gitlab-ci.yml

@@ -28,13 +28,18 @@ build-job:       # This job runs in the build stage, which runs first.
     - cmake --preset=ci .
     - cd /builds/DAPHNE4NFDI/build
     - ninja -j2
+  artifacts:
+    paths:
+      - "/builds/DAPHNE4NFDI/build"
 
 unit-test-job:   # This job runs in the test stage.
   stage: test    # It only starts when the job in the build stage completes successfully.
+  image: $CI_REGISTRY/daphne4nfdi/sassena:latest
+  dependencies:
+    - build-job
   script:
-    - echo "Running unit tests... This will take about 60 seconds."
-    - sleep 60
-    - echo "Code coverage is 90%"
+    - cd /builds/DAPHNE4NFDI/build
+    - ninja test
 
 lint-test-job:   # This job also runs in the test stage.
   stage: test    # It can run at the same time as unit-test-job (in parallel).