fix(ci): unset BUILDKIT_HOST in build stage script

The build stage script now unsets the BUILDKIT_HOST 
environment variable to ensure a clean build process. This 
prevents potential conflicts related to Docker BuildKit 
during the build.

.gitlab-ci.yml

@@ -14,5 +14,6 @@ build:
   stage: build
   script:
   - unset BUILDTOOLS_CONTENT
+  - unset BUILDKIT_HOST
   - build
   - push