doc: fix typos in async_context.md

PR-URL: #47155
Reviewed-By: Debadree Chatterjee <debadree333@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Deokjin Kim <deokjin81.kim@gmail.com>
Reviewed-By: Harshitha K P <harshitha014@gmail.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>

doc/api/async_context.md

@@ -167,7 +167,7 @@ calls the function passed to it within the captured context.
 
 ```js
 const asyncLocalStorage = new AsyncLocalStorage();
-const runInAsyncScope = asyncLocalStorage.run(123, () => asyncLocalStorage.snapshot());
+const runInAsyncScope = asyncLocalStorage.run(123, () => AsyncLocalStorage.snapshot());
 const result = asyncLocalStorage.run(321, () => runInAsyncScope(() => asyncLocalStorage.getStore()));
 console.log(result);  // returns 123
 ```