Update github-asset.ts

Proposed fix from coderabbitai

Author: tcely

src/github-asset.ts

@@ -63,24 +63,34 @@ export function getHexFromDigest(digest: GitHubDigest): string {
  * Latest: https://github.com/oven-sh/bun/releases/latest/download/bun-darwin-aarch64.zip
  */
 export function parseAssetUrl(downloadUrl: string): UrlAssetMetadata {
-  const url = new URL(downloadUrl);
+  const urlObj = new URL(downloadUrl);
+  if ("github.com" !== urlObj.hostname) {
+    throw new Error(`Expected a github.com URL, got: ${url.hostname}`);
+  }
+
   // Remove leading slash so index 0 is 'owner'
-  const parts = url.pathname.slice(1).split("/");
+  const parts = urlObj.pathname.slice(1).split("/");
+  if (parts.length < 6) {
+    throw new Error(`Unsupported GitHub asset URL format: ${downloadUrl}`);
+  }
+
+  const expectedStructure =
+    "releases" === parts[2] &&
+    ("latest" === parts[3] || "download" === parts[3]);
 
   const owner = parts[0];
   const repo = parts[1];
   let tag = parts[4];
   const name = parts[5];
 
-  if (!owner || !repo || !tag || !name) {
+  if (!expectedStructure || !owner || !repo || !tag || !name) {
     throw new Error(
       `Failed to parse GitHub asset metadata from: ${downloadUrl}`,
     );
   }
 
-  let latest = false;
-  if ("latest" === parts[3] && "download" === tag) {
-    latest = true;
+  const latest = "latest" === parts[3] && "download" === tag;
+  if (latest) {
     tag = "";
   }