.gitlab-ci.yml: Use --strict instead of list

This makes the output to be more compact while not loosing readability
--format=flycheck // --format=json could also be used but they are
not very human readable

.gitlab-ci.yml

@@ -42,4 +42,4 @@ unit-testing:
 analysis:
   stage: analysis
   script:
-    - mix credo list --only=warnings,todo,fixme,consistency,readability
+    - mix credo --strict --only=warnings,todo,fixme,consistency,readability