update.gitlab-ci.yml use export for variables in before_script

.gitlab-ci.yml

 image: ${CI_REGISTRY_IMAGE}/buildimage
 before_script:
-  - ARCH=all
-  - VERSION=$(dpkg-parsechangelog -S version)
-  - PKGNAME=$(awk '/^Package:/ { print $2 }' debian/control)
+  - export ARCH=all
+  - export VERSION=$(dpkg-parsechangelog -S version)
+  - export PKGNAME=$(awk '/^Package:/ { print $2 }' debian/control)
 
 .build-package: &build-package
   stage: test