fix: throw if the PHP version doesn't exist

src/SPC/store/source/PhpSource.php

@@ -35,6 +35,10 @@ class PhpSource extends CustomSourceBase
     {
         // 查找最新的小版本号
         $info = json_decode(Downloader::curlExec(url: "https://www.php.net/releases/index.php?json&version={$major_version}"), true);
+        if (!isset($info['version'])) {
+            throw new DownloaderException("Version {$major_version} not found.");
+        }
+
         $version = $info['version'];
 
         // 从官网直接下载