clear before_script for docker building stages

build/ci/.build-container.yml

@@ -7,6 +7,7 @@ variables:
   DOCKER_IMAGE_SHA: $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
 
 build:docker:
+  before_script:
   image: docker:19.03.12
   tags:
     - dind
@@ -23,6 +24,7 @@ build:docker:
         -t $DOCKER_IMAGE_SHA .
 
 .deploy: &deploy
+  before_script:
   image: docker:19.03.12
   stage: deploy
   needs: ["build:docker"]