adding resource group.

When many pipelines run at the same time, could cause some collision, false results, or not passing tests.
Restructured CI to avoid this from happening.

.gitlab/test2.yml

-stages:
-  - test
-
 run-test-job:
   stage: test
   script: echo "testing..."
   environment: testing
+  rules:
+    - if: $CI_PIPELINE_SOURCE == "parent_pipeline"