Make minimum version compatibility match the introduction of legacycustomsearches

Followup to !105 (merged) this will avoid somebody installing dataprocessor on an older site where they will be prompted to install legacycustomsearches that doesn't exist yet. It was added in 5.41 https://github.com/civicrm/civicrm-core/commit/191b5c818831a03969e8435063c6c7db6df8ae3c