[CI] Add YAML lint

.drone.yml

@@ -3,6 +3,11 @@ kind: pipeline
 name: latex
 
 steps:
+- name: yaml lint
+  image: cytopia/yamllint
+  commands:
+  - yamllint .drone.yml
+
 - name: build
   image: niccokunzmann/ci-latex
   commands:

.yamllint

@@ -0,0 +1,9 @@
+---
+extends: default
+
+rules:
+  indentation:
+    indent-sequences: consistent
+  line-length:
+    max: 120
+    level: warning