fix: add missing import after backport

Signed-off-by: Andrey Borysenko <andrey18106x@gmail.com>

lib/Fetcher/ExAppFetcher.php

@@ -12,6 +12,7 @@
 use OCP\AppFramework\Utility\ITimeFactory;
 use OCP\Http\Client\IClientService;
 use OCP\IConfig;
+use OCP\Server;
 use OCP\Support\Subscription\IRegistry;
 use Psr\Log\LoggerInterface;