Install yamllint for YAML linting by ansible-lint

https://github.com/ansible-community/ansible-lint/issues/953

.ansible-lint

 exclude_paths:
   - misc
 skip_list:
-  # Ignore lines longer than 160 chars
-  - '204'
+  # line too long (x > 80 characters) (line-length)
+  - 'line-length'
   # Do not recommend running tasks as handlers
   - '503'
   # Do not force galaxy info in meta/main.yml

.gitlab-ci.yml

 image: "archlinux:latest"
 
 before_script:
-  - pacman -Syu --needed --noconfirm ansible-lint terraform
+  - pacman -Syu --needed --noconfirm ansible-lint yamllint terraform
 
 ansible-lint:
   script: