RTC: Fix deleted-user test on multisite (#80463)

wp_delete_user() leaves the network user intact on multisite. Use the
multisite-aware test helper so the lock test deletes the user in both
configurations.

Co-authored-by: shekharnwagh <shekharnwagh@git.wordpress.org>
Co-authored-by: im3dabasia <im3dabasia1@git.wordpress.org>

Author: shekharnwagh

phpunit/tests/collaboration/quickEditCollaborationLock.php

@@ -59,7 +59,7 @@ private function prime_inline_save_request() {
 
 	public function test_deleted_user_lock_is_treated_as_inactive() {
 		$deleted_user_id = self::factory()->user->create();
-		wp_delete_user( $deleted_user_id );
+		self::delete_user( $deleted_user_id );
 		$this->set_edit_lock( $deleted_user_id );
 
 		$this->assertSame( 0, gutenberg_get_active_edit_lock_user( self::$post_id ), 'A lock from a deleted user should be inactive.' );