CI: replace deprecated only keyword with rules:if

* also, run tests on merge requests

.gitlab-ci.yml

@@ -12,6 +12,9 @@ run-tests:
     - pipenv run pip install -e '.[tests,opensearch2]'
     - pipenv run ./run-tests.sh
   coverage: /TOTAL.*? (100(?:\.0+)?\%|[1-9]?\d(?:\.\d+)?\%)$/
+  rules:
+    - if: $CI_PIPELINE_SOURCE == 'merge_request_event'
+    - if: $CI_COMMIT_BRANCH == '$CI_DEFAULT_BRANCH'
 
 sonarqube-check:
   stage: testing
@@ -25,9 +28,9 @@ sonarqube-check:
   script:
     - sonar-scanner
   allow_failure: true
-  only:
-    - master
-    - merge_requests
+  rules:
+    - if: $CI_PIPELINE_SOURCE == 'merge_request_event'
+    - if: $CI_COMMIT_BRANCH == '$CI_DEFAULT_BRANCH'
 
 pypi-release:
   stage: release