Update .gitlab-ci.yml

.gitlab-ci.yml

+stages:
+  - test
+  - docs
+
 before_script:
   # workaround for https://github.com/JuliaDocs/Documenter.jl/issues/686
   - apt-get -qq update; apt-get -y install git
@@ -31,18 +35,21 @@ before_script:
 
 Julia 1.6:
   image: julia:1.6
+  stage: test
   extends:
     - .script
     - .coverage
 
 Julia 1.8:
   image: julia:1.8
+  stage: test
   extends:
     - .script
     - .coverage
 
 docs:
   image: julia:1.6
+  stage: docs
   script:
     - |
       julia --project=docs -e '