If you specify rachetFrom and the branch doesn't exist locally, it should be fetched by the ratchet infrastructure.

https://github.com/JLLeitschuh/spotless/runs/1200916598?check_suite_focus=true#step:5:56

  [2020-10-02 21:07:06] [autobuild] * What went wrong:
  [2020-10-02 21:07:06] [autobuild] A problem occurred evaluating project ':ide'.
  [2020-10-02 21:07:06] [autobuild] > Could not create task ':lib:spotlessJava'.
  [2020-10-02 21:07:06] [autobuild]    > No such reference 'origin/main'

EDIT: Summary of workarounds from below

• GitHub Actions: add fetch-depth: 0 to <action>.yml
• GitLab CI: add GIT_DEPTH: 0 under the variables: section of .gitlab-ci.yml
• BitBucket Pipelines: clone: depth: full
• Travis: git: depth: false