Exclude runs on merge requests

Reference: https://docs.gitlab.com/ee/ci/yaml/README.html#prevent-duplicate-pipelines

gitlab-ci-template.yml

@@ -40,7 +40,7 @@ container-build-amd64:
   tags:
     - amd64
   rules:
-    - if: '$CI_CONTAINER_BUILD_ARCHS =~ /:?amd64:?/'
+    - if: '$CI_CONTAINER_BUILD_ARCHS =~ /:?amd64:?/ && $CI_PIPELINE_SOURCE != "merge_request_event"'
 
 container-build-arm64:
   extends: .container-build
@@ -49,7 +49,7 @@ container-build-arm64:
   tags:
     - arm64
   rules:
-    - if: '$CI_CONTAINER_BUILD_ARCHS =~ /:?arm64:?/'
+    - if: '$CI_CONTAINER_BUILD_ARCHS =~ /:?arm64:?/ && $CI_PIPELINE_SOURCE != "merge_request_event"'
 
 container-tagging:
   stage: tag