Issue #3470671: Skip role with isAdmin when save custom permission

Closes #3470671

src/Plugin/FieldPermissionType/CustomAccess.php

@@ -74,7 +74,11 @@ class CustomAccess extends Base implements CustomPermissionsInterface, AdminForm
     $custom_permissions = $form_state->getValue('permissions');
     $keys = array_keys($custom_permissions);
     $custom_permissions = $this->transposeArray($custom_permissions);
+    /** @var \Drupal\user\RoleInterface $role */
     foreach ($role_storage->loadMultiple() as $role) {
+      if ($role->isAdmin()) {
+        continue;
+      }
       $permissions = $role->getPermissions();
       $removed = array_values(array_intersect($permissions, $keys));
       $added = $this_plugin_applies ? array_keys(array_filter($custom_permissions[$role->id()])) : [];