Add --build-arg BUILDKIT_INLINE_CACHE=1

Reference: https://github.com/moby/buildkit/blob/master/README.md#inline-push-image-and-cache-together

.gitlab-ci.yml

@@ -37,7 +37,7 @@ build-master:
   stage: build
   script:
     - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
-    - DOCKER_BUILDKIT=1 docker build --pull -t "$CI_REGISTRY_IMAGE" .
+    - DOCKER_BUILDKIT=1 docker build --build-arg BUILDKIT_INLINE_CACHE=1 --pull -t "$CI_REGISTRY_IMAGE" .
     - docker push "$CI_REGISTRY_IMAGE"
   only:
     - master
@@ -46,7 +46,7 @@ build:
   stage: build
   script:
     - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
-    - DOCKER_BUILDKIT=1 docker build --pull -t "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG" .
+    - DOCKER_BUILDKIT=1 docker build --build-arg BUILDKIT_INLINE_CACHE=1 --pull -t "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG" .
     - docker push "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG"
   except:
     - master