fix(runtime): avoid infinite recursion in fetch for external URLs (#4153)

Author: vamsi2246

src/runtime/internal/app.ts

@@ -90,7 +90,7 @@ export function fetch(
     return serverFetch(resource, init, context);
   }
   resource = (resource as any)._request || resource; // unwrap srvx request
-  return fetch(resource, init);
+  return globalThis.fetch(resource, init);
 }
 
 function createNitroApp(): NitroApp {

test/fixture/server/routes/fetch.ts

@@ -10,6 +10,9 @@ export default async () => {
     ).then((res) => res.json()),
     "nitro/runtime.serverFetch": await runtimeServerFetch("/api/hello").then((res) => res.json()),
     "nitro/runtime.fetch": await runtimeFetch("/api/hello").then((res) => res.json()),
+    "nitro/runtime.fetch.url": await runtimeFetch(new URL("http://localhost/api/hello")).then(
+      (res) => res.json()
+    ),
     "nitro/serverFetch": await nitroServerFetch("/api/hello").then((res) => res.json()),
     "nitro/fetch": await nitroFetch("/api/hello").then((res) => res.json()),
   };