ci: do not run full backend ci when changin docs

Signed-off-by: Luca Zaninotto <luca.zaninotto@secomind.com>

Author: lusergit

.github/workflows/backend-ci.yaml

@@ -19,7 +19,6 @@
 name: Backend CI
 
 on:
-  # Run when pushing to stable branches
   push:
     paths:
       - "backend/**"
@@ -29,10 +28,10 @@ on:
       - "main"
       - "release-*"
       - "renovate/backend-*"
-  # Run on pull requests matching apps
   pull_request:
     paths:
       - "backend/**"
+      - "!backend/docs/**"
       - ".tool-versions"
       - ".github/workflows/backend-*.yaml"