docs/FAQ.md: Add js code fence syntax

docs/FAQ.md

@@ -46,7 +46,7 @@ if ( semver.lt(process.version, '20.0.0') ) {
 
 This is caused by the internal undici fetch implementation's dispatcher [defaults](https://github.com/nodejs/undici/issues/1373) for the headers and body timeout when performing a request. In the future we will support modifying these properties in a more defined way, but for now, once can override this by setting the global symbol at the beginning of your script:
 
-```
+```js
 import { Agent } from 'undici'
 
 globalThis[Symbol.for("undici.globalDispatcher.1")] = new Agent({