CI: Run yamllint on added or modified YAML files

Signed-off-by: Nils Philippsen <nils@redhat.com>

ci/yamllint-diff.yaml

@@ -0,0 +1,24 @@
+---
+- hosts: all
+  tasks:
+    - name: Install yamllint
+      package:
+        name: yamllint
+        state: latest
+
+    - name: Determine added or modified YAML files
+      command:
+        cmd: >
+          git diff --name-only --diff-filter=AM
+          origin/{{ zuul.branch|quote }}...{{ zuul.branch|quote }}
+      args:
+        chdir: '{{ zuul.project.src_dir }}'
+      register: fi_ansible__added_modified_yaml_files
+      changed_when: "False"
+      failed_when: fi_ansible__added_modified_yaml_files.rc != 0
+
+    - name: Run yamllint on changed YAML files
+      command: yamllint {{ item }}
+      args:
+        chdir: '{{ zuul.project.src_dir }}'
+      with_items: "{{ fi_ansible__added_modified_yaml_files.stdout_lines | list }}"