Fix UserPermissions unit test

Without having a current user, the permission would be `false` even if the logic test in `canChangeRole()` would not work, thus making the test useless; in fact just adding the impersonation made the test fail because manually creating a user object didn’t trigger the `isLastAdmin()` logic

tests/Cms/Users/UserPermissionsTest.php

@@ -122,16 +122,24 @@ public function testWithNoAdmin($action)
 
 	public function testChangeSingleRole()
 	{
-		new App([
+		$app = new App([
 			'roots' => [
 				'index' => '/dev/null'
 			],
 			'roles' => [
 				['name' => 'admin']
+			],
+			'users' => [
+				[
+					'email' => '[email protected]',
+					'role'  => 'admin'
+				]
 			]
 		]);
 
-		$user  = new User(['email' => '[email protected]']);
+		$app->impersonate('kirby');
+
+		$user  = $app->user('[email protected]');
 		$perms = $user->permissions();
 
 		$this->assertFalse($perms->can('changeRole'));