Drupal 9 compatibility

For compatibility with D9, add core_version_requirement: ^8 || ^9 to info.yml file. and Ran drupal-check & rector tools and scanned upgrade_status on barebones theme: No errors reported

my_site_name_dir % vendor/bin/drupal-check -ad web/themes/contrib/barebones        
    0 [▓▓▓░░░░░░░░░░░░░░░░░░░░░░░░░]


                                                                                                                        
 [OK] No errors                                                                                                         
                                                                                                                        

my_site_name_dir % vendor/bin/rector process web/themes/contrib/barebones          
Rector 0.8.x-dev@8896f0a
Config file: rector.yml


 [OK] Rector is done!