* 36807-gc-unwanted-refs-after-import:
  Use `git update-ref --stdin -z` to delete refs
  Just use a block
  Fix tests
  Try to make reserved ref names more obvious
  Resolve feedback on the MR:
  Move to Projects::HousecleaningService
  Use block rather than just b
  Just use @project directly
  Just use methods over constants, so that we could
  Add changelog and tests
  Remove unwanted refs after importing a project