Make APIv4 Subscribers Public to fix D9 install

[seamuslee001]

Overview

This fixes a failure on the D9 demo install

                                                                                                                                                                                                                                                         
  [CiviCRM_API3_Exception]                                                                                                                                                                                                                               
  The "Civi_Api4_Event_Subscriber_PermissionCheckSubscriber" service or alias has been removed or inlined when the container was compiled. You should either make it public, or stop using the container directly and use dependency injection instead.  
                                                                                                                                                                                                                                                         

Exception trace:
 () at /srv/buildkit/build/d9-master/vendor/civicrm/civicrm-core/api/api.php:134
 civicrm_api3() at /srv/buildkit/build/d9-master/vendor/civicrm/civicrm-core/CRM/Core/BAO/Setting.php:253
 CRM_Core_BAO_Setting::validateSettingsInput() at /srv/buildkit/build/d9-master/vendor/civicrm/civicrm-core/Civi/Core/SettingsBag.php:373
 Civi\Core\SettingsBag->setDb() at /srv/buildkit/build/d9-master/vendor/civicrm/civicrm-core/Civi/Core/SettingsBag.php:263

Before

This seems to be a slight regression from a9d469f and D9 demo build fails at this point

After

D9 Demo build installs CiviCRM correctly

ping @colemanw @totten @eileenmcnaughton

[civibot]

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[demeritcowboy]

I see this with a "regular" install of drupal 9 + civi (not just demo build) and the patch fixes it. But will let others confirm since I'm not fully up on the original issue.

[colemanw]

Fix seems simple & low-risk. Let's merge & see if that resolves things for the RC.