Support for PHP 8 (#2158)

painful 66 commits later: required PHP version bumped to 7.3, plugin updates using migrations necessary!

src/Ldap/LdapUserProvider.php

@@ -93,7 +93,7 @@ class LdapUserProvider implements UserProviderInterface
 
     public function supportsClass($class)
     {
-        return $class === User::class || $class === 'App\Entity\User';
+        return $class === User::class;
     }
 
     /**