fix: correct onError middleware syntax in docs

Fixes #2517

Removed nested onError function that caused TypeScript error.
The correct syntax is to directly return an Error instance from
the onError method, not nest another onError function inside it.

Author: lindseystead

docs/openapi-fetch/api.md

@@ -242,9 +242,7 @@ const myMiddleware: Middleware = {
   },
   async onError({ error }) {
     // wrap errors thrown by fetch
-    onError({ error }) {
-      return new Error("Oops, fetch failed", { cause: error });
-    },
+    return new Error("Oops, fetch failed", { cause: error });
   },
 };
 

docs/openapi-fetch/middleware-auth.md

@@ -29,9 +29,7 @@ const myMiddleware: Middleware = {
   },
   async onError({ error }) {
     // wrap errors thrown by fetch
-    onError({ error }) {
-      return new Error("Oops, fetch failed", { cause: error });
-    },
+    return new Error("Oops, fetch failed", { cause: error });
   },
 };