Split install/test/deploy to reduce artifacts size

.gitlab-ci.yml

-upstream_tests:
+install:
+  stage: install
   image: docker.io/node:current
-  before_script:
+  script:
     - npm ci
+  artifacts:
+    paths:
+      - node_modules
+
+upstream_tests:
+  stage: test
+  image: docker.io/node:current
   script:
     - npm run test:ci
   artifacts:
     when: always
     paths:
       - junit.xml
-      - node_modules
     reports:
       junit: junit.xml
 
 pages:
   stage: deploy
+  image: docker.io/node:current
   script:
     - npm run build
     - rm -rf public