Image build is optimized.

.gitlab-ci.yml

@@ -23,6 +23,8 @@ build:
   services:
     - docker:24-dind
   before_script:
+    - mkdir -p /mnt/volume
+    - mount /dev/vdb /mnt/volume
     - export DOCKER_TMPDIR=/mnt/volume
     - docker system prune -a -f
     - docker volume prune -f