Enable merge request pipeline

.gitlab/ci/_global.gitlab-ci.yml

@@ -9,6 +9,14 @@ variables:
   GIT_SSL_NO_VERIFY: 1
   DEBIAN_FRONTEND: noninteractive
 
+# See https://docs.gitlab.com/ee/ci/yaml/workflow.html#switch-between-branch-pipelines-and-merge-request-pipelines
+workflow:
+  rules:
+    - if: $CI_PIPELINE_SOURCE == "merge_request_event"
+    - if: $CI_COMMIT_BRANCH && $CI_OPEN_MERGE_REQUESTS
+      when: never
+    - if: $CI_COMMIT_BRANCH
+
 default:
   image: nvidia/cuda:12.2.0-devel-ubuntu22.04
   before_script: