More selective template linting.

Only on schedule or if the templates are changed.

.gitlab-ci.yml

@@ -31,6 +31,10 @@ lint templates:
     # yamllint enable rule:line-length
   variables:
     XDG_CACHE_HOME: "$CI_PROJECT_DIR/.cache"
+  rules:
+    - if: $CI_PIPELINE_SOURCE == "push"
+      changes:
+        - templates/*
   cache:
     paths:
       - .cache/