.gitlab-ci.yml: Adds credo to the chain

Not really sure about the order in which this is but it feels right
because credo is more about checking if a ~working code could need
some improvements.<M-1>

.gitlab-ci.yml

@@ -19,6 +19,7 @@ cache:
 stages:
   - lint
   - test
+  - analysis
 
 before_script:
   - mix local.hex --force
@@ -37,3 +38,8 @@ unit-testing:
   stage: test
   script:
     - mix test --trace --preload-modules
+
+analysis:
+  stage: analysis
+  script:
+    - mix credo list