ci(gitlab): switch npm to pnpm

- workaround for hexo issue
- doesn't affect renovate

.gitlab-ci.yml

@@ -4,15 +4,18 @@ cache: # add cache to 'node_modules' for speeding up builds
   paths:
     - node_modules/ # Node modules and dependencies
 
+variables:
+  NODE_ENV: "production"
+
 test:
   before_script:
     - 'which ssh-agent || (apk update && apk add openssh-client git)'
-    - npm install -g npm
-    - npm install --only=prod
+    - npm install -g pnpm
+    - pnpm install
 
   script:
-    - npm install snyk && npm run snyk # Refer to "scripts" in package.json
-    - npm run hexo
+    - pnpm install snyk && pnpm run snyk # Refer to "scripts" in package.json
+    - pnpm run hexo
 
   # Update github mirror
   after_script:
@@ -45,10 +48,10 @@ test:
 
 renovate: # Check dependency update
   before_script:
-    - npm install --only=prod
+    - npm install
 
   script:
-    - npm install --only=prod renovate
+    - npm install renovate
     - npm run renovate
 
   rules: