Renovate config validation error

Renovate config validator job from https://gitlab.com/sylva-projects/sylva-elements/diskimage-builder/-/jobs/11048860059 failed with:

INFO: Validating renovate.json
 WARN: Found errors in configuration
       "file": "renovate.json",
       "warnings": [
         {
           "topic": "Configuration Error",
           "message": "packageRules[0]: You must configure baseBranches inorder to use them inside matchBaseBranches."
         }
       ]