fix(ratelimit): Only use memory cache backend for redis

Signed-off-by: Anna Larch <anna@nextcloud.com>

lib/private/Server.php

@@ -796,8 +796,8 @@ class Server extends ServerContainer implements IServerContainer {
 		$this->registerDeprecatedAlias('Search', ISearch::class);
 
 		$this->registerService(\OC\Security\RateLimiting\Backend\IBackend::class, function ($c) {
-			$cacheFactory = $c->get(ICacheFactory::class);
-			if ($cacheFactory->isAvailable()) {
+			$config = $c->get(\OCP\IConfig::class);
+			if (ltrim($config->getSystemValueString('memcache.distributed', ''), '\\') === \OC\Memcache\Redis::class) {
 				$backend = new \OC\Security\RateLimiting\Backend\MemoryCacheBackend(
 					$c->get(AllConfig::class),
 					$this->get(ICacheFactory::class),