src: correct endif comment SRC_NODE_API_H__

Really minor but I could not find an open PR for anything n-api where
this could be changed, so creating this so that it is not forgotten.

Backport-PR-URL: #19447
PR-URL: #13190
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <mhdawson@ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/node_api.h

@@ -480,4 +480,4 @@ NAPI_EXTERN napi_status napi_cancel_async_work(napi_env env,
 
 EXTERN_C_END
 
-#endif  // SRC_NODE_API_H__
+#endif  // SRC_NODE_API_H_